diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 1c706785..4003b22e 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -64,8 +64,7 @@ jobs:
             parameters.txt
           retention-days: 7
 
-  # Build a cross compiler for Linux, targeting Windows.
-  linux:
+  linux-stage1:
     if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
     needs: [prepare]
     runs-on: ubuntu-22.04
@@ -82,7 +81,82 @@ jobs:
           # Skip dynamic library dependencies that might make it harder to
           # run the binaries on other distros (and that have little use within
           # llvm-mingw).
-          LLVM_CMAKEFLAGS="-DLLVM_ENABLE_LIBXML2=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $(pwd)/install/llvm-mingw
+          LLVM_CMAKEFLAGS="-DLLVM_ENABLE_LIBXML2=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $(pwd)/install/llvm-mingw --stage1
+          .github/workflows/store-version.sh install/llvm-mingw/versions.txt
+          ./test-libcxx-module.sh $(pwd)/install/llvm-mingw
+          ./run-tests.sh $(pwd)/install/llvm-mingw
+          cd install
+          DISTRO=ubuntu-$(grep DISTRIB_RELEASE /etc/lsb-release | cut -f 2 -d =)-$(uname -m)
+          NAME=llvm-mingw-stage1-$TAG-ucrt-$DISTRO
+          mv llvm-mingw $NAME
+          tar -Jcf ../$NAME.tar.xz --format=ustar --numeric-owner --owner=0 --group=0 --sort=name --mtime="$BUILD_DATE" $NAME
+      - uses: actions/upload-artifact@v4
+        with:
+          name: linux-stage1-ucrt-x86_64-toolchain
+          path: |
+            llvm-mingw-*.tar.xz
+          retention-days: 7
+
+  linux-profile:
+    if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
+    needs: [prepare, linux-stage1]
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/download-artifact@v4
+        with:
+          name: linux-stage1-ucrt-x86_64-toolchain
+      - name: Unpack stage1 Clang
+        run: |
+          tar -Jxf llvm-mingw-*.tar.xz
+          rm llvm-mingw-*.tar.xz
+          mv llvm-mingw* llvm-mingw-stage1
+      - name: Build
+        env:
+          LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
+          TAG: ${{needs.prepare.outputs.TAG}}
+          SOURCE_DATE_EPOCH: ${{needs.prepare.outputs.COMMIT_DATE_UNIX}}
+          BUILD_DATE: ${{needs.prepare.outputs.BUILD_DATE}}
+        run: |
+          # Build LLVM in mostly the same way as it is going to be built in the
+          # final form.
+          LLVM_CMAKEFLAGS="-DLLVM_ENABLE_LIBXML2=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh --profile $(pwd)/llvm-mingw-stage1
+      - uses: actions/upload-artifact@v4
+        with:
+          name: profile
+          path: |
+            profile.profdata
+          retention-days: 7
+
+  # Build a cross compiler for Linux, targeting Windows.
+  linux:
+    if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
+    needs: [prepare, linux-stage1, linux-profile]
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/download-artifact@v4
+        with:
+          name: linux-stage1-ucrt-x86_64-toolchain
+      - name: Unpack stage1 Clang
+        run: |
+          tar -Jxf llvm-mingw-*.tar.xz
+          rm llvm-mingw-*.tar.xz
+          sudo mv llvm-mingw* /opt/llvm-mingw
+      - uses: actions/download-artifact@v4
+        with:
+          name: profile
+      - name: Build
+        env:
+          LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
+          TAG: ${{needs.prepare.outputs.TAG}}
+          SOURCE_DATE_EPOCH: ${{needs.prepare.outputs.COMMIT_DATE_UNIX}}
+          BUILD_DATE: ${{needs.prepare.outputs.BUILD_DATE}}
+        run: |
+          # Skip dynamic library dependencies that might make it harder to
+          # run the binaries on other distros (and that have little use within
+          # llvm-mingw).
+          LLVM_CMAKEFLAGS="-DLLVM_ENABLE_LIBXML2=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw --thinlto --pgo --llvm-only
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
           ./test-libcxx-module.sh $(pwd)/install/llvm-mingw
           ./run-tests.sh $(pwd)/install/llvm-mingw
@@ -102,10 +176,21 @@ jobs:
   # libraries that were built in the 'linux' step above.
   linux-cross-aarch64:
     if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
-    needs: [linux, prepare]
+    needs: [linux-stage1, linux-profile, prepare]
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v4
+      - uses: actions/download-artifact@v4
+        with:
+          name: linux-stage1-ucrt-x86_64-toolchain
+      - name: Unpack stage1 Clang
+        run: |
+          tar -Jxf llvm-mingw-*.tar.xz
+          rm llvm-mingw-*.tar.xz
+          sudo mv llvm-mingw* /opt/llvm-mingw
+      - uses: actions/download-artifact@v4
+        with:
+          name: profile
       - name: Build
         env:
           LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
@@ -113,19 +198,11 @@ jobs:
           SOURCE_DATE_EPOCH: ${{needs.prepare.outputs.COMMIT_DATE_UNIX}}
         run: |
           sudo apt-get update && sudo apt-get install g++-aarch64-linux-gnu
-          ./build-all.sh $(pwd)/install/llvm-mingw --no-runtimes --host=aarch64-linux-gnu
+          ./build-all.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw --no-runtimes --host=aarch64-linux-gnu --thinlto --pgo
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
-      - uses: actions/download-artifact@v4
-        with:
-          name: linux-ucrt-x86_64-toolchain
-      - name: Unpack native toolchain
-        run: |
-          tar -Jxf llvm-mingw-*.tar.xz
-          rm llvm-mingw-*.tar.xz
-          mv llvm-mingw* llvm-mingw-native
       - name: Assemble the cross-built toolchain
         run: |
-          ./prepare-cross-toolchain-unix.sh $(pwd)/llvm-mingw-native $(pwd)/install/llvm-mingw
+          ./prepare-cross-toolchain-unix.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw
       - name: Test using the cross-built assembled toolchain
         run: |
           sudo apt-get update && sudo apt-get install qemu-user-static libc6-arm64-cross libstdc++6-arm64-cross
@@ -183,13 +260,53 @@ jobs:
             llvm-mingw-linux.tar.xz
           retention-days: 7
 
+  macos-stage1:
+    if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
+    needs: [prepare]
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Build
+        env:
+          LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
+          TAG: ${{needs.prepare.outputs.TAG}}
+          SOURCE_DATE_EPOCH: ${{needs.prepare.outputs.COMMIT_DATE_UNIX}}
+          BUILD_DATE: ${{needs.prepare.outputs.BUILD_DATE}}
+        run: |
+          # Disable zstd and python. Both are available on the runners, but
+          # installed with homebrew, and only available in the native (arm64)
+          # form.
+          LLVM_CMAKEFLAGS="-DLLVM_ENABLE_ZSTD=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $(pwd)/install/llvm --stage1 --llvm-only
+          .github/workflows/store-version.sh install/llvm/versions.txt
+          cd install
+          NAME=llvm-$TAG-macos-$(uname -m)
+          mv llvm $NAME
+          gtar -Jcf ../$NAME.tar.xz --format=ustar --numeric-owner --owner=0 --group=0 --sort=name --mtime="$BUILD_DATE" $NAME
+      - uses: actions/upload-artifact@v4
+        with:
+          name: macos-llvm
+          path: |
+            llvm-*.tar.xz
+          retention-days: 7
+
   # Build a cross compiler for macOS, targeting Windows.
   macos:
     if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
-    needs: [prepare]
+    needs: [prepare, macos-stage1, linux-profile]
     runs-on: macos-latest
     steps:
       - uses: actions/checkout@v4
+      - uses: actions/download-artifact@v4
+        with:
+          name: macos-llvm
+      - name: Unpack stage1 Clang
+        run: |
+          tar -Jxf llvm-*.tar.xz
+          rm llvm-*.tar.xz
+          mv llvm* $HOME/llvm
+      - uses: actions/download-artifact@v4
+        with:
+          name: profile
       - name: Build
         env:
           LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
@@ -203,7 +320,7 @@ jobs:
           # form. Therefore, autodetection will pick them up, but linking
           # universal binaries fails as those libraries are unavailable in the
           # other (x86_64) architecture form.
-          MACOS_REDIST=1 LLVM_CMAKEFLAGS="-DLLVM_ENABLE_ZSTD=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $(pwd)/install/llvm-mingw
+          MACOS_REDIST=1 LLVM_CMAKEFLAGS="-DLLVM_ENABLE_ZSTD=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $HOME/llvm $(pwd)/install/llvm-mingw --thinlto --pgo
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
           ./test-libcxx-module.sh $(pwd)/install/llvm-mingw
           ./run-tests.sh $(pwd)/install/llvm-mingw
@@ -280,7 +397,7 @@ jobs:
   # architectures). The binaries built here match actual releases quite closely.
   linux-cross-windows:
     if: (github.event_name != 'schedule') || (github.repository == 'mstorsjo/llvm-mingw')
-    needs: [linux, prepare]
+    needs: [linux-stage1, linux-profile, prepare]
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
@@ -293,7 +410,7 @@ jobs:
     steps:
       - uses: actions/download-artifact@v4
         with:
-          name: linux-${{matrix.crt}}-x86_64-toolchain
+          name: linux-stage1-${{matrix.crt}}-x86_64-toolchain
       - name: Unpack cross toolchain
         run: |
           tar -Jxf llvm-mingw-*.tar.xz
@@ -301,6 +418,9 @@ jobs:
           sudo mv llvm-mingw* /opt/llvm-mingw
           echo /opt/llvm-mingw/bin >> $GITHUB_PATH
       - uses: actions/checkout@v4
+      - uses: actions/download-artifact@v4
+        with:
+          name: profile
       - name: Build
         env:
           LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
@@ -311,7 +431,7 @@ jobs:
           BUILD_DATE: ${{needs.prepare.outputs.BUILD_DATE}}
         run: |
           sudo apt-get update && sudo apt-get install libltdl-dev swig autoconf-archive
-          ./build-cross-tools.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw ${{matrix.arch}} --with-python
+          ./build-cross-tools.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw ${{matrix.arch}} --with-python --thinlto --pgo
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
           cd install
           NAME=llvm-mingw-$TAG-${{matrix.crt}}-${{matrix.arch}}
@@ -689,6 +809,9 @@ jobs:
         run: |
           rm -rf linux-asserts*
           rm -rf msys2*
+          rm -rf linux-stage1-*
+          rm -rf macos-llvm*
+          rm -rf profile*
           mv *-toolchain/*.zip *-toolchain/*.tar.xz .
       - name: Upload binaries
         env:
diff --git a/.github/workflows/docker.yml b/.github/workflows/docker.yml
index 411a20be..c992bb54 100644
--- a/.github/workflows/docker.yml
+++ b/.github/workflows/docker.yml
@@ -64,18 +64,11 @@ jobs:
   docker-build:
     needs: [prepare]
     runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - { file: Dockerfile, key: amd64 }
-          - { file: Dockerfile.toolchain, platforms: linux/arm64, key: arm64 }
     steps:
       - uses: actions/checkout@v4
         with:
           ref: ${{inputs.ref}}
       - name: Download toolchain
-        if: ${{matrix.file == 'Dockerfile.toolchain'}}
         uses: dawidd6/action-download-artifact@v10
         with:
           workflow: build.yml
@@ -86,7 +79,6 @@ jobs:
           name_is_regexp: true
           path: toolchain
       - name: Set up QEMU
-        if: ${{matrix.file == 'Dockerfile.toolchain'}}
         uses: docker/setup-qemu-action@v3
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
@@ -98,42 +90,11 @@ jobs:
           password: ${{secrets.DOCKER_PASSWORD}}
       - name: Build Docker images
         uses: docker/build-push-action@v5
-        id: build
         with:
           context: .
-          platforms: ${{matrix.platforms}}
+          platforms: linux/amd64,linux/arm64
           push: ${{inputs.push}}
-          file: ./${{matrix.file}}
-          outputs: |
-            type=image,name=mstorsjo/llvm-mingw,push-by-digest=true,name-canonical=true
-      - name: Write outputs for later steps
-        uses: cloudposse/github-action-matrix-outputs-write@main
-        id: out
-        with:
-          matrix-step-name: ${{github.job}}
-          matrix-key: ${{matrix.key}}
-          outputs: |-
-            digest: ${{steps.build.outputs.digest}}
-
-  docker-create:
-    needs: [docker-build, prepare]
-    runs-on: ubuntu-latest
-    if: ${{inputs.push}}
-    steps:
-      - uses: cloudposse/github-action-matrix-outputs-read@main
-        id: read
-        with:
-          matrix-step-name: docker-build
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@v3
-      - name: Log in to Docker Hub
-        uses: docker/login-action@v3
-        with:
-          username: ${{vars.DOCKER_USERNAME}}
-          password: ${{secrets.DOCKER_PASSWORD}}
-      - name: Create final image
-        run: |
-          set -x
-          for tag in latest ${{needs.prepare.outputs.TAG}}; do
-              docker buildx imagetools create -t mstorsjo/llvm-mingw:$tag mstorsjo/llvm-mingw@${{fromJson(steps.read.outputs.result).digest.amd64}} mstorsjo/llvm-mingw@${{fromJson(steps.read.outputs.result).digest.arm64}}
-          done
+          file: ./Dockerfile.toolchain
+          tags: |
+            mstorsjo/llvm-mingw:latest
+            mstorsjo/llvm-mingw:${{needs.prepare.outputs.TAG}}
diff --git a/.github/workflows/msvcrt.yml b/.github/workflows/msvcrt.yml
index 9fb12761..ff0856e4 100644
--- a/.github/workflows/msvcrt.yml
+++ b/.github/workflows/msvcrt.yml
@@ -106,6 +106,14 @@ jobs:
       - uses: actions/checkout@v4
         with:
           ref: ${{inputs.ref}}
+      - name: Download profile
+        uses: dawidd6/action-download-artifact@v6
+        with:
+          workflow: build.yml
+          workflow_conclusion: success
+          ref: ${{inputs.ref}}
+          event: push
+          name: profile
       - name: Build
         env:
           LLVM_VERSION: ${{needs.prepare.outputs.LLVM_VERSION}}
@@ -114,7 +122,7 @@ jobs:
           TAG: ${{needs.prepare.outputs.TAG}}
         run: |
           sudo apt-get update && sudo apt-get install libltdl-dev swig autoconf-archive
-          ./build-cross-tools.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw ${{matrix.arch}} --with-python
+          ./build-cross-tools.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw ${{matrix.arch}} --with-python --thinlto --pgo
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
           cd install
           NAME=llvm-mingw-$TAG-${{matrix.crt}}-${{matrix.arch}}
diff --git a/build-all.sh b/build-all.sh
index 42c21e04..39bfa676 100755
--- a/build-all.sh
+++ b/build-all.sh
@@ -24,7 +24,7 @@ HOST_ARGS=""
 
 while [ $# -gt 0 ]; do
     case "$1" in
-    --enable-asserts)
+    --enable-asserts|--disable-dylib|--with-clang|--thinlto)
         LLVM_ARGS="$LLVM_ARGS $1"
         ;;
     --host-clang|--host-clang=*)
@@ -36,9 +36,6 @@ while [ $# -gt 0 ]; do
         LLVM_ARGS="$LLVM_ARGS $1"
         FULL_LLVM=1
         ;;
-    --disable-dylib)
-        LLVM_ARGS="$LLVM_ARGS $1"
-        ;;
     --disable-lldb)
         LLVM_ARGS="$LLVM_ARGS $1"
         NO_LLDB=1
@@ -76,18 +73,58 @@ while [ $# -gt 0 ]; do
     --clean-runtimes)
         CLEAN_RUNTIMES=1
         ;;
+    --llvm-only)
+        LLVM_ONLY=1
+        ;;
+    --stage1)
+        STAGE1=1
+        LLVM_ARGS="$LLVM_ARGS --disable-lldb --disable-clang-tools-extra"
+        NO_LLDB=1
+        ;;
+    --profile|--profile=*)
+        case "$1" in
+        --profile=*)
+            INSTRUMENTATION="=${1#*=}"
+            ;;
+        esac
+        PROFILE=1
+        LLVM_ARGS="$LLVM_ARGS --disable-lldb --disable-clang-tools-extra --with-clang --disable-dylib --instrumented$INSTRUMENTATION"
+        NO_LLDB=1
+        LLVM_ONLY=1
+        ;;
+    --pgo|--pgo=*)
+        PGO=1
+        LLVM_ARGS="$LLVM_ARGS --with-clang $1"
+        ;;
+    --full-pgo|--full-pgo=*)
+        case "$1" in
+        --full-pgo=*)
+            INSTRUMENTATION="=${1#*=}"
+            ;;
+        esac
+        PGO=1
+        FULL_PGO=1
+        ;;
     *)
         if [ -n "$PREFIX" ]; then
-            echo Unrecognized parameter $1
-            exit 1
+            if [ -n "$PREFIX_PGO" ]; then
+                echo Unrecognized parameter $1
+                exit 1
+            fi
+            PREFIX_PGO="$1"
+        else
+            PREFIX="$1"
         fi
-        PREFIX="$1"
         ;;
     esac
     shift
 done
 if [ -z "$PREFIX" ]; then
-    echo "$0 [--host-clang[=clang]] [--enable-asserts] [--disable-dylib] [--full-llvm] [--disable-lldb] [--disable-lldb-mi] [--disable-clang-tools-extra] [--host=triple] [--with-default-win32-winnt=0x601] [--with-default-msvcrt=ucrt] [--enable-cfguard|--disable-cfguard] [--no-runtimes] [--no-tools] [--wipe-runtimes] [--clean-runtimes] dest"
+    echo "$0 [--host-clang[=clang]] [--enable-asserts] [--disable-dylib] [--with-clang] [--thinlto] [--full-llvm] [--disable-lldb] [--disable-lldb-mi] [--disable-clang-tools-extra] [--host=triple] [--with-default-win32-winnt=0x601] [--with-default-msvcrt=ucrt] [--enable-cfguard|--disable-cfguard] [--no-runtimes] [--llvm-only] [--no-tools] [--wipe-runtimes] [--clean-runtimes] [--stage1] [--profile[=type]] [--pgo[=profile]] [--full-pgo[=type]] dest [pgo-dest]"
+    exit 1
+fi
+if [ -n "$PREFIX_PGO" ] && [ -z "$PGO" ] && [ -z "$FULL_PGO" ]; then
+    echo Unrecognized parameter $1
     exit 1
 fi
 
@@ -102,15 +139,83 @@ if [ -n "${HOST_CLANG}" ] && [ "${CFGUARD_ARGS}" = "--enable-cfguard"  ]; then
     "${HOST_CLANG}" -c -x c -o - - -Werror -mguard=cf </dev/null >/dev/null 2>/dev/null || CFGUARD_ARGS="--disable-cfguard"
 fi
 
+if [ -n "$FULL_PGO" ]; then
+    if [ -z "$PREFIX_PGO" ]; then
+        echo Must provide a second destination for a PGO build
+        exit 1
+    fi
+    ./build-all.sh "$PREFIX" --stage1 $LLVM_ARGS $MINGW_ARGS $CFGUARD_ARGS
+    unset COMPILER_LAUNCHER
+    ./build-all.sh "$PREFIX" --profile$INSTRUMENTATION $LLVM_ARGS
+    ./build-all.sh "$PREFIX" "$PREFIX_PGO" --thinlto --pgo --llvm-only $LLVM_ARGS
+    # If one already has a usable profile, one could also do the following
+    # two steps only:
+    # ./build-all.sh "$PREFIX" --stage1 --llvm-only
+    # ./build-all.sh "$PREFIX" "$PREFIX_PGO" --pgo
+    exit 0
+fi
+
+if [ -n "$PROFILE" ]; then
+    export PATH=$PREFIX/bin:$PATH
+    STAGE1_PREFIX=$PREFIX
+    PREFIX=/tmp/dummy-prefix
+elif [ -n "$PGO" ]; then
+    if [ -z "$PREFIX_PGO" ]; then
+        echo Must provide a second destination for a PGO build
+        exit 1
+    fi
+    export PATH=$PREFIX/bin:$PATH
+    STAGE1_PREFIX=$PREFIX
+    PREFIX=$PREFIX_PGO
+
+    if [ -n "$LLVM_ONLY" ] && [ "$PREFIX" != "$STAGE1_PREFIX" ] ; then
+        # Only rebuilding LLVM, not any runtimes. Copy the stage1 toolchain
+        # and rebuild LLVM on top of it.
+        rm -rf $PREFIX
+        mkdir -p "$(dirname "$PREFIX")"
+        cp -a "$STAGE1_PREFIX" "$PREFIX"
+        # Remove the native Linux/macOS runtimes which aren't needed in
+        # the final distribution.
+        rm -rf "$PREFIX"/lib/clang/*/lib/darwin
+        rm -rf "$PREFIX"/lib/clang/*/lib/linux
+    fi
+fi
+
+if [ "$(uname)" = "Darwin" ]; then
+    if [ -n "$PROFILE" ] || [ -n "$PGO" ]; then
+        # Using a custom Clang, which doesn't find the SDK automatically.
+        # CMake sets this automatically, but if using the compiler directly,
+        # this is needed. (If compilation uses "cc" or "gcc", it will miss
+        # the stage1 llvm-mingw toolchain and use the system compiler anyway.)
+        export SDKROOT=$(xcrun --show-sdk-path)
+    fi
+fi
+
 if [ -z "$NO_TOOLS" ]; then
     if [ -z "${HOST_CLANG}" ]; then
         ./build-llvm.sh $PREFIX $LLVM_ARGS $HOST_ARGS
+        if [ -n "$PROFILE" ]; then
+            ./pgo-training.sh llvm-project/llvm/build-instrumented $STAGE1_PREFIX
+            exit 0
+        fi
         if [ -z "$NO_LLDB" ] && [ -z "$NO_LLDB_MI" ]; then
             ./build-lldb-mi.sh $PREFIX $HOST_ARGS
         fi
         if [ -z "$FULL_LLVM" ]; then
             ./strip-llvm.sh $PREFIX $HOST_ARGS
         fi
+        if [ -n "$STAGE1" ]; then
+            if [ "$(uname)" = "Darwin" ]; then
+                ./build-llvm.sh $PREFIX --macos-native-tools
+            fi
+            # Build runtimes. On Linux, this is needed for profiling.
+            # On macOS, it is also needed for OS availability helpers like
+            # __isPlatformVersionAtLeast.
+            ./build-compiler-rt.sh --native $PREFIX
+        fi
+    fi
+    if [ -n "$LLVM_ONLY" ]; then
+        exit 0
     fi
     ./install-wrappers.sh $PREFIX $HOST_ARGS ${HOST_CLANG:+--host-clang=$HOST_CLANG}
     ./build-mingw-w64-tools.sh $PREFIX $HOST_ARGS
diff --git a/build-compiler-rt.sh b/build-compiler-rt.sh
index d7f3e3d7..89c8d722 100755
--- a/build-compiler-rt.sh
+++ b/build-compiler-rt.sh
@@ -40,13 +40,16 @@ while [ $# -gt 0 ]; do
     elif [ "$1" = "--disable-cfguard" ]; then
         CFGUARD_CFLAGS=
         ENABLE_CFGUARD=
+    elif [ "$1" = "--native" ]; then
+        NATIVE=1
+        SRC_DIR=..
     else
         PREFIX="$1"
     fi
     shift
 done
 if [ -z "$PREFIX" ]; then
-    echo "$0 [--build-sanitizers] [--enable-cfguard|--disable-cfguard] dest"
+    echo "$0 [--build-sanitizers] [--enable-cfguard|--disable-cfguard] [--native] dest"
     exit 1
 fi
 if [ -n "$SANITIZERS" ] && [ -n "$ENABLE_CFGUARD" ]; then
@@ -59,8 +62,7 @@ export PATH="$PREFIX/bin:$PATH"
 
 : ${ARCHS:=${TOOLCHAIN_ARCHS-i686 x86_64 armv7 aarch64}}
 
-ANY_ARCH=$(echo $ARCHS | awk '{print $1}')
-CLANG_RESOURCE_DIR="$("$PREFIX/bin/$ANY_ARCH-w64-mingw32-clang" --print-resource-dir)"
+CLANG_RESOURCE_DIR="$("$PREFIX/bin/clang" --print-resource-dir)"
 
 if [ ! -d llvm-project/compiler-rt ] || [ -n "$SYNC" ]; then
     CHECKOUT_ONLY=1 ./build-llvm.sh
@@ -91,6 +93,34 @@ if [ -h "$CLANG_RESOURCE_DIR/include" ]; then
     INSTALL_PREFIX="$WORKDIR/install"
 fi
 
+if [ -n "$NATIVE" ]; then
+    [ -z "$CLEAN" ] || rm -rf build-native
+    mkdir -p build-native
+    cd build-native
+    [ -n "$NO_RECONF" ] || rm -rf CMake*
+    cmake \
+        ${CMAKE_GENERATOR+-G} "$CMAKE_GENERATOR" \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_INSTALL_PREFIX="$CLANG_RESOURCE_DIR" \
+        -DCMAKE_C_COMPILER=clang \
+        -DCMAKE_CXX_COMPILER=clang++ \
+        -DLLVM_CONFIG_PATH="" \
+        -DCMAKE_FIND_ROOT_PATH=$PREFIX \
+        -DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY \
+        -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ONLY \
+        -DCOMPILER_RT_USE_LIBCXX=OFF \
+        $SRC_DIR
+    cmake --build . ${CORES:+-j${CORES}}
+    cmake --install . --prefix "$INSTALL_PREFIX"
+
+    if [ "$INSTALL_PREFIX" != "$CLANG_RESOURCE_DIR" ]; then
+        # symlink to system headers - skip copy
+        rm -rf "$INSTALL_PREFIX/include"
+
+        cp -r "$INSTALL_PREFIX/." $CLANG_RESOURCE_DIR
+    fi
+    exit 0
+fi
 
 for arch in $ARCHS; do
     [ -z "$CLEAN" ] || rm -rf build-$arch$BUILD_SUFFIX
diff --git a/build-cross-tools.sh b/build-cross-tools.sh
index 1aa94804..fd28ec71 100755
--- a/build-cross-tools.sh
+++ b/build-cross-tools.sh
@@ -44,6 +44,9 @@ while [ $# -gt 0 ]; do
     --disable-make)
         NO_MAKE=1
         ;;
+    --thinlto|--lto|--pgo*)
+        LLVM_ARGS="$LLVM_ARGS $1"
+        ;;
     *)
         if [ -z "$NATIVE" ]; then
             NATIVE="$1"
@@ -60,7 +63,7 @@ while [ $# -gt 0 ]; do
     shift
 done
 if [ -z "$CROSS_ARCH" ]; then
-    echo $0 native prefix arch [--with-python] [--disable-lldb] [--disable-lldb-mi] [--disable-clang-tool-extra] [--disable-mingw-w64-tools] [--disable-make]
+    echo $0 native prefix arch [--with-python] [--disable-lldb] [--disable-lldb-mi] [--disable-clang-tool-extra] [--disable-mingw-w64-tools] [--disable-make] [--thinlto] [--lto] [--pgo[=profile]]
     exit 1
 fi
 
diff --git a/build-lldb-mi.sh b/build-lldb-mi.sh
index 7c228213..1dd6b13d 100755
--- a/build-lldb-mi.sh
+++ b/build-lldb-mi.sh
@@ -65,7 +65,7 @@ else
     esac
 fi
 
-export LLVM_DIR="$PREFIX"
+LLVM_DIR="$PREFIX"
 
 # Try to find/guess the builddir under the llvm buildtree next by.
 # If LLVM was built without LLVM_INSTALL_TOOLCHAIN_ONLY, and the LLVM
@@ -75,12 +75,32 @@ export LLVM_DIR="$PREFIX"
 LLVM_SRC="$(pwd)/llvm-project/llvm"
 if [ -d "$LLVM_SRC" ]; then
     SUFFIX=${HOST+-}$HOST
-    for base in build build-asserts; do
-        if [ -d "$LLVM_SRC/$base$SUFFIX" ]; then
-            export LLVM_DIR="$LLVM_SRC/$base$SUFFIX"
-            break
+    DIRS=""
+    cd llvm-project/llvm
+    for dir in build*$SUFFIX; do
+        if [ -z "$SUFFIX" ]; then
+            case $dir in
+            *linux*|*mingw32*)
+                continue
+                ;;
+            esac
+        fi
+        if [ -d "$dir" ]; then
+            DIRS="$DIRS $dir"
         fi
     done
+    if [ -n "$DIRS" ]; then
+        dir="$(ls -td $DIRS | head -1)"
+        LLVM_DIR="$LLVM_SRC/$dir"
+        echo Using $LLVM_DIR as LLVM build dir
+        break
+    else
+        # No build directory found; this is ok if the installed prefix is a
+        # full (development) install of LLVM. Warn that we didn't find what
+        # we were looking for.
+        echo Warning, did not find a suitable LLVM build dir, assuming $PREFIX contains LLVM development files >&2
+    fi
+    cd ../..
 fi
 
 if [ -n "$HOST" ]; then
@@ -101,14 +121,14 @@ if [ -n "$HOST" ]; then
         exit 1
         ;;
     esac
-
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH=$LLVM_DIR"
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER"
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY"
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_LIBRARY=ONLY"
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ONLY"
 fi
 
+CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH=$LLVM_DIR"
+CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER"
+CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY"
+CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_LIBRARY=ONLY"
+CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ONLY"
+
 if [ -n "$MACOS_REDIST" ]; then
     : ${MACOS_REDIST_ARCHS:=arm64 x86_64}
     : ${MACOS_REDIST_VERSION:=10.12}
diff --git a/build-llvm.sh b/build-llvm.sh
index de2c4a43..9f21b713 100755
--- a/build-llvm.sh
+++ b/build-llvm.sh
@@ -24,6 +24,7 @@ LINK_DYLIB=ON
 ASSERTSSUFFIX=""
 LLDB=ON
 CLANG_TOOLS_EXTRA=ON
+INSTRUMENTED=OFF
 
 while [ $# -gt 0 ]; do
     case "$1" in
@@ -35,9 +36,9 @@ while [ $# -gt 0 ]; do
         ASSERTS=ON
         ASSERTSSUFFIX="-asserts"
         ;;
-    --stage2)
-        STAGE2=1
-        BUILDDIR="$BUILDDIR-stage2"
+    --with-clang)
+        WITH_CLANG=1
+        BUILDDIR="$BUILDDIR-withclang"
         ;;
     --thinlto)
         LTO="thin"
@@ -68,6 +69,31 @@ while [ $# -gt 0 ]; do
     --no-llvm-tool-reuse)
         NO_LLVM_TOOL_REUSE=1
         ;;
+    --macos-native-tools)
+        MACOS_NATIVE_TOOLS=1
+        ;;
+    --instrumented|--instrumented=*)
+        INSTRUMENTED="${1#--instrumented}"
+        INSTRUMENTED="${INSTRUMENTED#=}"
+        INSTRUMENTED="${INSTRUMENTED:-Frontend}"
+        : ${LLVM_PROFILE_DATA_DIR:=/tmp/llvm-profile}
+        # A fixed BUILDDIR is set at the end for this case.
+        ;;
+    --pgo|--pgo=*)
+        case "$1" in
+        --pgo=*)
+            LLVM_PROFDATA_FILE="${1#--pgo}"
+            LLVM_PROFDATA_FILE="${LLVM_PROFDATA_FILE#=}"
+            ;;
+        esac
+        LLVM_PROFDATA_FILE="${LLVM_PROFDATA_FILE:-profile.profdata}"
+        if [ ! -e "$LLVM_PROFDATA_FILE" ]; then
+            echo Profile \"$LLVM_PROFDATA_FILE\" not found
+            exit 1
+        fi
+        LLVM_PROFDATA_FILE="$(cd "$(dirname "$LLVM_PROFDATA_FILE")" && pwd)/$(basename "$LLVM_PROFDATA_FILE")"
+        BUILDDIR="$BUILDDIR-pgo"
+        ;;
     *)
         PREFIX="$1"
         ;;
@@ -77,12 +103,14 @@ done
 BUILDDIR="$BUILDDIR$ASSERTSSUFFIX"
 if [ -z "$CHECKOUT_ONLY" ]; then
     if [ -z "$PREFIX" ]; then
-        echo $0 [--enable-asserts] [--stage2] [--thinlto] [--lto] [--disable-dylib] [--full-llvm] [--with-python] [--disable-lldb] [--disable-clang-tools-extra] [--host=triple] dest
+        echo $0 [--enable-asserts] [--with-clang] [--thinlto] [--lto] [--instrumented[=type]] [--pgo[=profile]] [--disable-dylib] [--full-llvm] [--with-python] [--disable-lldb] [--disable-clang-tools-extra] [--host=triple] [--macos-native-tools] dest
         exit 1
     fi
 
-    mkdir -p "$PREFIX"
-    PREFIX="$(cd "$PREFIX" && pwd)"
+    if [ -z "$INSTRUMENTED" ]; then
+        mkdir -p "$PREFIX"
+        PREFIX="$(cd "$PREFIX" && pwd)"
+    fi
 fi
 
 if [ ! -d llvm-project ]; then
@@ -157,9 +185,18 @@ CMAKEFLAGS="$LLVM_CMAKEFLAGS"
 
 if [ -n "$HOST" ]; then
     ARCH="${HOST%%-*}"
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_C_COMPILER=$HOST-gcc"
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_CXX_COMPILER=$HOST-g++"
-    CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_SYSTEM_PROCESSOR=$ARCH"
+
+    if [ -n "$WITH_CLANG" ]; then
+        CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_C_COMPILER=clang"
+        CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_CXX_COMPILER=clang++"
+        CMAKEFLAGS="$CMAKEFLAGS -DLLVM_USE_LINKER=lld"
+        CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_C_COMPILER_TARGET=$HOST"
+        CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_CXX_COMPILER_TARGET=$HOST"
+    else
+        CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_C_COMPILER=$HOST-gcc"
+        CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_CXX_COMPILER=$HOST-g++"
+        CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_SYSTEM_PROCESSOR=$ARCH"
+    fi
     case $HOST in
     *-mingw32)
         CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_SYSTEM_NAME=Windows"
@@ -220,9 +257,9 @@ if [ -n "$HOST" ]; then
         CMAKEFLAGS="$CMAKEFLAGS -DPython3_INCLUDE_DIRS=$PYTHON_INCLUDE_DIR"
         CMAKEFLAGS="$CMAKEFLAGS -DPython3_LIBRARIES=$PYTHON_LIB"
     fi
-elif [ -n "$STAGE2" ]; then
-    # Build using an earlier built and installed clang in the target directory
-    export PATH="$PREFIX/bin:$PATH"
+elif [ -n "$WITH_CLANG" ]; then
+    # Build using clang and lld (from $PATH), rather than the system default
+    # tools.
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_C_COMPILER=clang"
     CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_CXX_COMPILER=clang++"
     CMAKEFLAGS="$CMAKEFLAGS -DLLVM_USE_LINKER=lld"
@@ -289,6 +326,25 @@ if [ -z "$HOST" ] && [ "$(uname)" = "Darwin" ]; then
         # This silences a cmake warning.
         CMAKEFLAGS="$CMAKEFLAGS -DLLDB_USE_SYSTEM_DEBUGSERVER=ON"
     fi
+    if [ -n "$WITH_CLANG" ] && [ -n "$LTO" ]; then
+        # If doing LTO, we need to make sure other related tools are used.
+        # CMAKE_LIBTOOL is not a standard cmake tool, but an LLVM specific
+        # thing. It defaults to looking up the tool with xcrun rather than
+        # looking in paths first.
+        # If building for multiple architectures at once
+        # (CMAKE_OSX_ARCHITECTURES), we also need to provide a tool named
+        # "lipo" in the PATH (this is invoked by Clang directly, so we can't
+        # specify it here unless we pass in the option "-fuse-lipo="). If
+        # the LLVM CMake build wasn't using libtool, we would also need to
+        # specify LLVM_AR and LLVM_RANLIB.
+        CMAKEFLAGS="$CMAKEFLAGS -DCMAKE_LIBTOOL=$(command -v llvm-libtool-darwin)"
+    fi
+fi
+
+if [ "$INSTRUMENTED" != "OFF" ]; then
+    # For instrumented build, use a hardcoded builddir that we can
+    # locate, and don't install the built files.
+    BUILDDIR="build-instrumented"
 fi
 
 TOOLCHAIN_ONLY=ON
@@ -309,6 +365,24 @@ fi
 [ -z "$CLEAN" ] || rm -rf $BUILDDIR
 mkdir -p $BUILDDIR
 cd $BUILDDIR
+
+if [ -n "$MACOS_NATIVE_TOOLS" ]; then
+    # Build tools needed for targeting macOS with LTO.
+    #
+    # The install-<tool>(-stripped) targets are unavailable for
+    # tools that are excluded due to LLVM_INSTALL_TOOLCHAIN_ONLY=ON and
+    # LLVM_TOOLCHAIN_TOOLS, so install those manually.
+    cmake --build . --target llvm-lipo --target llvm-libtool-darwin
+    # Install ld64.lld, required for -fuse-ld=lld
+    cmake --install . --strip --component lld
+    # Install llvm-libtool-darwin and lipo, needed for building with LTO.
+    # See the comment further above for more details about this.
+    cp bin/llvm-lipo bin/llvm-libtool-darwin $PREFIX/bin
+    strip $PREFIX/bin/llvm-lipo $PREFIX/bin/llvm-libtool-darwin
+    ln -sf llvm-lipo $PREFIX/bin/lipo
+    exit 0
+fi
+
 [ -n "$NO_RECONF" ] || rm -rf CMake*
 cmake \
     ${CMAKE_GENERATOR+-G} "$CMAKE_GENERATOR" \
@@ -321,10 +395,19 @@ cmake \
     -DLLVM_LINK_LLVM_DYLIB=$LINK_DYLIB \
     -DLLVM_TOOLCHAIN_TOOLS="llvm-ar;llvm-ranlib;llvm-objdump;llvm-rc;llvm-cvtres;llvm-nm;llvm-strings;llvm-readobj;llvm-dlltool;llvm-pdbutil;llvm-objcopy;llvm-strip;llvm-cov;llvm-profdata;llvm-addr2line;llvm-symbolizer;llvm-windres;llvm-ml;llvm-readelf;llvm-size;llvm-cxxfilt;llvm-lib" \
     ${HOST+-DLLVM_HOST_TRIPLE=$HOST} \
+    -DLLVM_BUILD_INSTRUMENTED=$INSTRUMENTED \
+    ${LLVM_PROFILE_DATA_DIR+-DLLVM_PROFILE_DATA_DIR=$LLVM_PROFILE_DATA_DIR} \
+    ${LLVM_PROFDATA_FILE+-DLLVM_PROFDATA_FILE=$LLVM_PROFDATA_FILE} \
     $CMAKEFLAGS \
     ..
 
-cmake --build . ${CORES:+-j${CORES}}
-cmake --install . --strip
+if [ "$INSTRUMENTED" != "OFF" ]; then
+    # For instrumented builds, don't install the built files (so $PREFIX
+    # is entirely unused).
+    cmake --build . ${CORES:+-j${CORES}} --target clang --target lld
+else
+    cmake --build . ${CORES:+-j${CORES}}
+    cmake --install . --strip
 
-cp ../LICENSE.TXT $PREFIX
+    cp ../LICENSE.TXT $PREFIX
+fi
diff --git a/pgo-training.make b/pgo-training.make
new file mode 100755
index 00000000..b26bc029
--- /dev/null
+++ b/pgo-training.make
@@ -0,0 +1,57 @@
+#!/bin/sh
+#
+# Copyright (c) 2025 Martin Storsjo
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+CFLAGS = --sysroot=$(STAGE1) -resource-dir=$(shell $(STAGE1)/bin/clang --print-resource-dir) --config-user-dir=$(STAGE1)/bin
+CC = $(PREFIX)/bin/clang
+CXX = $(PREFIX)/bin/clang++
+
+hello-exception-opt-%.exe: test/hello-exception.cpp
+	$(CXX) -target $*-w64-mingw32 $(CFLAGS) $+ -o $@ -O3
+
+hello-exception-%.exe: test/hello-exception.cpp
+	$(CXX) -target $*-w64-mingw32 $(CFLAGS) $+ -o $@
+
+sqlite-opt-%.exe: $(SQLITE)/sqlite3.c $(SQLITE)/shell.c
+	$(CC) -target $*-w64-mingw32 $(CFLAGS) $+ -o $@ -O3
+
+sqlite-%.exe: $(SQLITE)/sqlite3.c $(SQLITE)/shell.c
+	$(CC) -target $*-w64-mingw32 $(CFLAGS) $+ -o $@
+
+LIBCXXTEST = llvm-project/libcxx/test/std/algorithms/alg.sorting/alg.sort/sort/sort.pass.cpp
+
+libcxxtest-opt-%.exe: $(LIBCXXTEST)
+	$(CXX) -target $*-w64-mingw32 $(CFLAGS) $+ -o $@ -Illvm-project/libcxx/test/support -O3
+
+libcxxtest-%.exe: $(LIBCXXTEST)
+	$(CXX) -target $*-w64-mingw32 $(CFLAGS) $+ -o $@ -Illvm-project/libcxx/test/support
+
+ARCHS ?= i686 x86_64 armv7 aarch64
+
+TARGETS = hello-exception hello-exception-opt
+
+ifneq ($(SQLITE),)
+TARGETS += sqlite sqlite-opt
+endif
+ifneq ($(wildcard $(LIBCXXTEST)),)
+TARGETS += libcxxtest libcxxtest-opt
+endif
+
+ALLTARGETS = $(foreach arch, $(ARCHS), $(foreach target, $(TARGETS), $(target)-$(arch).exe))
+
+all: $(ALLTARGETS)
+
+clean:
+	rm -f $(ALLTARGETS)
diff --git a/pgo-training.sh b/pgo-training.sh
new file mode 100755
index 00000000..918e0e55
--- /dev/null
+++ b/pgo-training.sh
@@ -0,0 +1,63 @@
+#!/bin/sh
+#
+# Copyright (c) 2025 Martin Storsjo
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+set -e
+
+: ${SQLITE_VERSION:=3490200}
+: ${SQLITE_YEAR:=2025}
+
+: ${LLVM_PROFILE_DATA_DIR:=/tmp/llvm-profile}
+: ${LLVM_PROFDATA_FILE:=profile.profdata}
+
+if [ $# -lt 2 ]; then
+    echo $0 build stage1
+    exit 1
+fi
+PREFIX="$1"
+STAGE1="$2"
+PREFIX="$(cd "$PREFIX" && pwd)"
+
+MAKE=make
+if command -v gmake >/dev/null; then
+    MAKE=gmake
+fi
+
+: ${CORES:=$(nproc 2>/dev/null)}
+: ${CORES:=$(sysctl -n hw.ncpu 2>/dev/null)}
+: ${CORES:=4}
+: ${ARCHS:=${TOOLCHAIN_ARCHS-i686 x86_64 armv7 aarch64}}
+
+download() {
+    if command -v curl >/dev/null; then
+        curl -LO "$1"
+    else
+        wget "$1"
+    fi
+}
+
+SQLITE=sqlite-amalgamation-$SQLITE_VERSION
+if [ ! -d $SQLITE ]; then
+    download https://sqlite.org/$SQLITE_YEAR/sqlite-amalgamation-$SQLITE_VERSION.zip
+    unzip sqlite-amalgamation-$SQLITE_VERSION.zip
+fi
+
+rm -rf "$LLVM_PROFILE_DATA_DIR"
+$MAKE -f pgo-training.make PREFIX=$PREFIX STAGE1=$STAGE1 SQLITE=$SQLITE clean
+$MAKE -f pgo-training.make PREFIX=$PREFIX STAGE1=$STAGE1 SQLITE=$SQLITE -j$CORES
+
+rm -f "$LLVM_PROFDATA_FILE"
+$STAGE1/bin/llvm-profdata merge -output "$LLVM_PROFDATA_FILE" $LLVM_PROFILE_DATA_DIR/*.profraw
+rm -rf "$LLVM_PROFILE_DATA_DIR"