[DirectX] Legalize memcpy #139173

Icohedron · 2025-05-08T23:46:17Z

This PR legalizes memcpy for DXIL in cases where:

the src and dst arguments are from Alloca or a GlobalVariable,
the src and dst are pointers to an ArrayType,
the array element types of src and dst must be equivalent, and
the len param is a ConstantInt

These assumptions simplify the legalization and, with the addition of #138991, covers the currently-known cases of memcpy that appear when compiling DML shaders.

This PR may be unnecessary if #138788 determines that memset and memcpy can be eliminated entirely.

llvmbot · 2025-05-08T23:46:52Z

@llvm/pr-subscribers-backend-directx

Author: Deric C. (Icohedron)

Changes

Fixes #137188

This PR legalizes memcpy for DXIL in cases where:

the src and dst arguments are from Alloca or a GlobalVariable,
the types of the src and dst must be equivalent, and
the len param is a ConstantInt

These assumption simplify the legalization and, with the addition of #138991, covers the currently-known cases of memcpy that appear when compiling DML shaders.

Full diff: https://github.com/llvm/llvm-project/pull/139173.diff

2 Files Affected:

(modified) llvm/lib/Target/DirectX/DXILLegalizePass.cpp (+78)
(added) llvm/test/CodeGen/DirectX/legalize-memcpy.ll (+174)

diff --git a/llvm/lib/Target/DirectX/DXILLegalizePass.cpp b/llvm/lib/Target/DirectX/DXILLegalizePass.cpp
index be77a70fa46ba..d9e560a9f8859 100644
--- a/llvm/lib/Target/DirectX/DXILLegalizePass.cpp
+++ b/llvm/lib/Target/DirectX/DXILLegalizePass.cpp
@@ -15,6 +15,7 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Pass.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include <functional>
 
@@ -246,6 +247,58 @@ downcastI64toI32InsertExtractElements(Instruction &I,
   }
 }
 
+static void emitMemcpyExpansion(IRBuilder<> &Builder, Value *Dst, Value *Src,
+                                ConstantInt *Length) {
+
+  uint64_t ByteLength = Length->getZExtValue();
+  if (ByteLength == 0)
+    return;
+
+  LLVMContext &Ctx = Builder.getContext();
+  const DataLayout &DL = Builder.GetInsertBlock()->getModule()->getDataLayout();
+
+  auto GetArrTyFromVal = [](Value *Val) {
+    if (auto *Alloca = dyn_cast<AllocaInst>(Val))
+      return dyn_cast<ArrayType>(Alloca->getAllocatedType());
+    if (auto *GlobalVar = dyn_cast<GlobalVariable>(Val))
+      return dyn_cast<ArrayType>(GlobalVar->getValueType());
+    llvm_unreachable(
+        "Expected an Alloca or GlobalVariable in memcpy Src and Dst");
+  };
+
+  ArrayType *ArrTy = GetArrTyFromVal(Dst);
+  assert(ArrTy && "Expected Dst of memcpy to be a Pointer to an Array Type");
+  if (auto *DstGlobalVar = dyn_cast<GlobalVariable>(Dst))
+    assert(!DstGlobalVar->isConstant() &&
+           "The Dst of memcpy must not be a constant Global Variable");
+
+  [[maybe_unused]] ArrayType *SrcArrTy = GetArrTyFromVal(Src);
+  assert(SrcArrTy && "Expected Src of memcpy to be a Pointer to an Array Type");
+
+  // This assumption simplifies implementation and covers currently-known
+  // use-cases for DXIL. It may be relaxed in the future if required.
+  assert(ArrTy == SrcArrTy && "Array Types of Src and Dst in memcpy must match");
+
+  Type *ElemTy = ArrTy->getElementType();
+  uint64_t ElemSize = DL.getTypeStoreSize(ElemTy);
+  assert(ElemSize > 0 && "Size must be set");
+
+  [[maybe_unused]] uint64_t Size = ArrTy->getArrayNumElements();
+  assert(ElemSize * Size >= ByteLength &&
+         "Array size must be at least as large as the memcpy length");
+
+  uint64_t NumElemsToCopy = ByteLength / ElemSize;
+  assert(ByteLength % ElemSize == 0 &&
+         "memcpy length must be divisible by array element type");
+  for (uint64_t I = 0; I < NumElemsToCopy; ++I) {
+    Value *Offset = ConstantInt::get(Type::getInt32Ty(Ctx), I);
+    Value *SrcPtr = Builder.CreateGEP(ElemTy, Src, Offset, "gep");
+    Value *SrcVal = Builder.CreateLoad(ElemTy, SrcPtr);
+    Value *DstPtr = Builder.CreateGEP(ElemTy, Dst, Offset, "gep");
+    Builder.CreateStore(SrcVal, DstPtr);
+  }
+}
+
 static void emitMemsetExpansion(IRBuilder<> &Builder, Value *Dst, Value *Val,
                                 ConstantInt *SizeCI,
                                 DenseMap<Value *, Value *> &ReplacedValues) {
@@ -296,6 +349,30 @@ static void emitMemsetExpansion(IRBuilder<> &Builder, Value *Dst, Value *Val,
   }
 }
 
+static void removeMemCpy(Instruction &I,
+                         SmallVectorImpl<Instruction *> &ToRemove,
+                         DenseMap<Value *, Value *> &ReplacedValues) {
+
+  CallInst *CI = dyn_cast<CallInst>(&I);
+  if (!CI)
+    return;
+
+  Intrinsic::ID ID = CI->getIntrinsicID();
+  if (ID != Intrinsic::memcpy)
+    return;
+
+  IRBuilder<> Builder(&I);
+  Value *Dst = CI->getArgOperand(0);
+  Value *Src = CI->getArgOperand(1);
+  ConstantInt *Length = dyn_cast<ConstantInt>(CI->getArgOperand(2));
+  assert(Length && "Expected Length to be a ConstantInt");
+  ConstantInt *IsVolatile = dyn_cast<ConstantInt>(CI->getArgOperand(3));
+  assert(IsVolatile && "Expected IsVolatile to be a ConstantInt");
+  assert(IsVolatile->getZExtValue() == 0 && "Expected IsVolatile to be false");
+  emitMemcpyExpansion(Builder, Dst, Src, Length);
+  ToRemove.push_back(CI);
+}
+
 static void removeMemSet(Instruction &I,
                          SmallVectorImpl<Instruction *> &ToRemove,
                          DenseMap<Value *, Value *> &ReplacedValues) {
@@ -348,6 +425,7 @@ class DXILLegalizationPipeline {
     LegalizationPipeline.push_back(fixI8UseChain);
     LegalizationPipeline.push_back(downcastI64toI32InsertExtractElements);
     LegalizationPipeline.push_back(legalizeFreeze);
+    LegalizationPipeline.push_back(removeMemCpy);
     LegalizationPipeline.push_back(removeMemSet);
   }
 };
diff --git a/llvm/test/CodeGen/DirectX/legalize-memcpy.ll b/llvm/test/CodeGen/DirectX/legalize-memcpy.ll
new file mode 100644
index 0000000000000..09a4d051a2822
--- /dev/null
+++ b/llvm/test/CodeGen/DirectX/legalize-memcpy.ll
@@ -0,0 +1,174 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -dxil-legalize -dxil-finalize-linkage -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s
+
+@outputStrides = external local_unnamed_addr addrspace(2) global [2 x <4 x i32>], align 4
+
+define void @replace_2x4xint_global_memcpy_test() #0 {
+; CHECK-LABEL: define void @replace_2x4xint_global_memcpy_test(
+; CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    [[TMP1:%.*]] = alloca [2 x <4 x i32>], align 16
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 32, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    [[TMP2:%.*]] = load <4 x i32>, ptr addrspace(2) @outputStrides, align 16
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr <4 x i32>, ptr [[TMP1]], i32 0
+; CHECK-NEXT:    store <4 x i32> [[TMP2]], ptr [[GEP]], align 16
+; CHECK-NEXT:    [[TMP3:%.*]] = load <4 x i32>, ptr addrspace(2) getelementptr (<4 x i32>, ptr addrspace(2) @outputStrides, i32 1), align 16
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr <4 x i32>, ptr [[TMP1]], i32 1
+; CHECK-NEXT:    store <4 x i32> [[TMP3]], ptr [[GEP1]], align 16
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 32, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    ret void
+;
+  %1 = alloca [2 x <4 x i32>], align 16
+  call void @llvm.lifetime.start.p0(i64 32, ptr nonnull %1)
+  call void @llvm.memcpy.p0.p2.i32(ptr nonnull align 16 dereferenceable(32) %1, ptr addrspace(2) align 16 dereferenceable(32) @outputStrides, i32 32, i1 false)
+  call void @llvm.lifetime.end.p0(i64 32, ptr nonnull %1)
+  ret void
+}
+
+define void @replace_int_memcpy_test() #0 {
+; CHECK-LABEL: define void @replace_int_memcpy_test(
+; CHECK-SAME: ) #[[ATTR0]] {
+; CHECK-NEXT:    [[TMP1:%.*]] = alloca [1 x i32], align 4
+; CHECK-NEXT:    [[TMP2:%.*]] = alloca [1 x i32], align 4
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 4, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 4, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i32, ptr [[TMP1]], i32 0
+; CHECK-NEXT:    [[TMP3:%.*]] = load i32, ptr [[GEP]], align 4
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr i32, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    store i32 [[TMP3]], ptr [[GEP1]], align 4
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    ret void
+;
+  %1 = alloca [1 x i32], align 4
+  %2 = alloca [1 x i32], align 4
+  call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %1)
+  call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %2)
+  call void @llvm.memcpy.p0.p0.i32(ptr nonnull align 4 dereferenceable(4) %2, ptr align 4 dereferenceable(4) %1, i32 4, i1 false)
+  call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %2)
+  call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %1)
+  ret void
+}
+
+define void @replace_int16_memcpy_test() #0 {
+; CHECK-LABEL: define void @replace_int16_memcpy_test(
+; CHECK-SAME: ) #[[ATTR0]] {
+; CHECK-NEXT:    [[TMP1:%.*]] = alloca [2 x i16], align 2
+; CHECK-NEXT:    [[TMP2:%.*]] = alloca [2 x i16], align 2
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 4, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 4, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i16, ptr [[TMP1]], i32 0
+; CHECK-NEXT:    [[TMP3:%.*]] = load i16, ptr [[GEP]], align 2
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr i16, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    store i16 [[TMP3]], ptr [[GEP1]], align 2
+; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr i16, ptr [[TMP1]], i32 1
+; CHECK-NEXT:    [[TMP4:%.*]] = load i16, ptr [[GEP2]], align 2
+; CHECK-NEXT:    [[GEP3:%.*]] = getelementptr i16, ptr [[TMP2]], i32 1
+; CHECK-NEXT:    store i16 [[TMP4]], ptr [[GEP3]], align 2
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    ret void
+;
+  %1 = alloca [2 x i16], align 2
+  %2 = alloca [2 x i16], align 2
+  call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %1)
+  call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %2)
+  call void @llvm.memcpy.p0.p0.i32(ptr nonnull align 2 dereferenceable(4) %2, ptr align 2 dereferenceable(4) %1, i32 4, i1 false)
+  call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %2)
+  call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %1)
+  ret void
+}
+
+define void @replace_float_memcpy_test() #0 {
+; CHECK-LABEL: define void @replace_float_memcpy_test(
+; CHECK-SAME: ) #[[ATTR0]] {
+; CHECK-NEXT:    [[TMP1:%.*]] = alloca [2 x float], align 4
+; CHECK-NEXT:    [[TMP2:%.*]] = alloca [2 x float], align 4
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 8, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 8, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr float, ptr [[TMP1]], i32 0
+; CHECK-NEXT:    [[TMP3:%.*]] = load float, ptr [[GEP]], align 4
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr float, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    store float [[TMP3]], ptr [[GEP1]], align 4
+; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr float, ptr [[TMP1]], i32 1
+; CHECK-NEXT:    [[TMP4:%.*]] = load float, ptr [[GEP2]], align 4
+; CHECK-NEXT:    [[GEP3:%.*]] = getelementptr float, ptr [[TMP2]], i32 1
+; CHECK-NEXT:    store float [[TMP4]], ptr [[GEP3]], align 4
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 8, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 8, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    ret void
+;
+  %1 = alloca [2 x float], align 4
+  %2 = alloca [2 x float], align 4
+  call void @llvm.lifetime.start.p0(i64 8, ptr nonnull %1)
+  call void @llvm.lifetime.start.p0(i64 8, ptr nonnull %2)
+  call void @llvm.memcpy.p0.p0.i32(ptr nonnull align 4 dereferenceable(8) %2, ptr align 4 dereferenceable(8) %1, i32 8, i1 false)
+  call void @llvm.lifetime.end.p0(i64 8, ptr nonnull %2)
+  call void @llvm.lifetime.end.p0(i64 8, ptr nonnull %1)
+  ret void
+}
+
+define void @replace_double_memcpy_test() #0 {
+; CHECK-LABEL: define void @replace_double_memcpy_test(
+; CHECK-SAME: ) #[[ATTR0]] {
+; CHECK-NEXT:    [[TMP1:%.*]] = alloca [2 x double], align 4
+; CHECK-NEXT:    [[TMP2:%.*]] = alloca [2 x double], align 4
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 16, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 16, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr double, ptr [[TMP1]], i32 0
+; CHECK-NEXT:    [[TMP3:%.*]] = load double, ptr [[GEP]], align 8
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr double, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    store double [[TMP3]], ptr [[GEP1]], align 8
+; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr double, ptr [[TMP1]], i32 1
+; CHECK-NEXT:    [[TMP4:%.*]] = load double, ptr [[GEP2]], align 8
+; CHECK-NEXT:    [[GEP3:%.*]] = getelementptr double, ptr [[TMP2]], i32 1
+; CHECK-NEXT:    store double [[TMP4]], ptr [[GEP3]], align 8
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 16, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 16, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    ret void
+;
+  %1 = alloca [2 x double], align 4
+  %2 = alloca [2 x double], align 4
+  call void @llvm.lifetime.start.p0(i64 16, ptr nonnull %1)
+  call void @llvm.lifetime.start.p0(i64 16, ptr nonnull %2)
+  call void @llvm.memcpy.p0.p0.i32(ptr nonnull align 4 dereferenceable(8) %2, ptr align 4 dereferenceable(8) %1, i32 16, i1 false)
+  call void @llvm.lifetime.end.p0(i64 16, ptr nonnull %2)
+  call void @llvm.lifetime.end.p0(i64 16, ptr nonnull %1)
+  ret void
+}
+
+define void @replace_half_memcpy_test() #0 {
+; CHECK-LABEL: define void @replace_half_memcpy_test(
+; CHECK-SAME: ) #[[ATTR0]] {
+; CHECK-NEXT:    [[TMP1:%.*]] = alloca [2 x half], align 2
+; CHECK-NEXT:    [[TMP2:%.*]] = alloca [2 x half], align 2
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 4, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 4, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr half, ptr [[TMP1]], i32 0
+; CHECK-NEXT:    [[TMP3:%.*]] = load half, ptr [[GEP]], align 2
+; CHECK-NEXT:    [[GEP1:%.*]] = getelementptr half, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    store half [[TMP3]], ptr [[GEP1]], align 2
+; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr half, ptr [[TMP1]], i32 1
+; CHECK-NEXT:    [[TMP4:%.*]] = load half, ptr [[GEP2]], align 2
+; CHECK-NEXT:    [[GEP3:%.*]] = getelementptr half, ptr [[TMP2]], i32 1
+; CHECK-NEXT:    store half [[TMP4]], ptr [[GEP3]], align 2
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[TMP2]])
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[TMP1]])
+; CHECK-NEXT:    ret void
+;
+  %1 = alloca [2 x half], align 2
+  %2 = alloca [2 x half], align 2
+  call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %1)
+  call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %2)
+  call void @llvm.memcpy.p0.p0.i32(ptr nonnull align 2 dereferenceable(4) %2, ptr align 2 dereferenceable(4) %1, i32 4, i1 false)
+  call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %2)
+  call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %1)
+  ret void
+}
+
+attributes #0 = {"hlsl.export"}
+
+
+declare void @llvm.lifetime.end.p0(i64 immarg, ptr captures(none))
+declare void @llvm.lifetime.start.p0(i64 immarg, ptr captures(none))
+declare void @llvm.memcpy.p0.p2.i32(ptr noalias, ptr addrspace(2) noalias readonly, i32, i1)
+declare void @llvm.memcpy.p0.p0.i32(ptr noalias, ptr noalias readonly, i32, i1)

llvm/lib/Target/DirectX/DXILLegalizePass.cpp

Co-authored-by: Finn Plummer <[email protected]>

llvm/lib/Target/DirectX/DXILLegalizePass.cpp

farzonl · 2025-05-15T17:46:08Z

llvm/test/CodeGen/DirectX/legalize-memcpy.ll

+; CHECK-NEXT:    ret void
+;
+  %1 = alloca [2 x <4 x i32>], align 16
+  call void @llvm.lifetime.start.p0(i64 32, ptr nonnull %1)


Do we need the life times for the global scope memory? I know they are always there for allocas, was not sure if they impacted global memory.

@pow2clk just suggested not having lifetime markers at all because they're not explicitly being tested here, and I do agree. So I will be removing all the lifetime markers from the test.

llvm/lib/Target/DirectX/DXILLegalizePass.cpp

pow2clk

Looks good! I really don't have any issues with the functionality, just some commenting, naming, testing suggestions and a question about when this pass is run.

pow2clk · 2025-05-15T16:30:47Z

llvm/lib/Target/DirectX/DXILLegalizePass.cpp

@@ -348,6 +427,7 @@ class DXILLegalizationPipeline {
    LegalizationPipeline.push_back(fixI8UseChain);
    LegalizationPipeline.push_back(downcastI64toI32InsertExtractElements);
    LegalizationPipeline.push_back(legalizeFreeze);
+    LegalizationPipeline.push_back(removeMemCpy);


I know it's just copying the removeMemSet, but I think that's a bad description of what this does. It isn't just removing the memcpy, but expanding/legalizing it. Is there a reason not to call this what the change does, "legalizeMemCpy"?

I don't think there is a good reason not to call it "legalizeMemCpy". I just followed what @farzonl did for memset.
I think "legalizeMemCpy" is a better name, so I will make a commit to change it to that.

llvm/lib/Target/DirectX/DXILLegalizePass.cpp

pow2clk · 2025-05-15T18:46:27Z

llvm/test/CodeGen/DirectX/legalize-memcpy.ll

+; CHECK-NEXT:    ret void
+;
+  %1 = alloca [2 x <4 x i32>], align 16
+  call void @llvm.lifetime.start.p0(i64 32, ptr nonnull %1)


I don't know the tendencies for testing here, but I've taken to removing lifetime markers when I'm not testing them directly. That would simplify some of you CHECK walls of text somewhat.

llvm/test/CodeGen/DirectX/legalize-memcpy.ll

Co-authored-by: Greg Roth <[email protected]>

Legalize memcpy

a23c221

llvmbot added the backend:DirectX label May 8, 2025

Apply clang-format

6ab5c90

inbelic approved these changes May 9, 2025

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Icohedron and others added 2 commits May 9, 2025 12:16

Specify return type of lambda expression

8d12237

Co-authored-by: Finn Plummer <[email protected]>

Replace llvm_unreachable with assert

b44152e