[profcheck][SimplifyCFG] Propagate !prof from `switch` to `select` #159645

mtrofin · 2025-09-18T20:14:07Z

Propagate !prof from switch instructions.

Issue #147390

mtrofin · 2025-09-18T20:14:25Z

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github-actions · 2025-09-18T20:17:57Z

✅ With the latest revision this PR passed the C/C++ code formatter.

llvmbot · 2025-09-18T20:18:35Z

@llvm/pr-subscribers-llvm-transforms

Author: Mircea Trofin (mtrofin)

Changes

Patch is 21.02 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/159645.diff

2 Files Affected:

(modified) llvm/lib/Transforms/Utils/SimplifyCFG.cpp (+75-11)
(modified) llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll (+42-30)

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index a1f759dd1df83..276ca89d715f1 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -84,6 +84,7 @@
 #include <cstdint>
 #include <iterator>
 #include <map>
+#include <numeric>
 #include <optional>
 #include <set>
 #include <tuple>
@@ -6318,9 +6319,12 @@ static bool initializeUniqueCases(SwitchInst *SI, PHINode *&PHI,
 // Helper function that checks if it is possible to transform a switch with only
 // two cases (or two cases + default) that produces a result into a select.
 // TODO: Handle switches with more than 2 cases that map to the same result.
+// The branch weights correspond to the provided Condition (i.e. if Condition is
+// modified from the original SwitchInst, the caller must adjust the weights)
 static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
                                  Constant *DefaultResult, Value *Condition,
-                                 IRBuilder<> &Builder, const DataLayout &DL) {
+                                 IRBuilder<> &Builder, const DataLayout &DL,
+                                 ArrayRef<uint32_t> BranchWeights) {
   // If we are selecting between only two cases transform into a simple
   // select or a two-way select if default is possible.
   // Example:
@@ -6329,6 +6333,10 @@ static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
   //   case 20: return 2;   ---->  %2 = icmp eq i32 %a, 20
   //   default: return 4;          %3 = select i1 %2, i32 2, i32 %1
   // }
+
+  const bool HasBranchWeights =
+      !BranchWeights.empty() && !ProfcheckDisableMetadataFixes;
+
   if (ResultVector.size() == 2 && ResultVector[0].second.size() == 1 &&
       ResultVector[1].second.size() == 1) {
     ConstantInt *FirstCase = ResultVector[0].second[0];
@@ -6337,13 +6345,37 @@ static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
     if (DefaultResult) {
       Value *ValueCompare =
           Builder.CreateICmpEQ(Condition, SecondCase, "switch.selectcmp");
-      SelectValue = Builder.CreateSelect(ValueCompare, ResultVector[1].first,
-                                         DefaultResult, "switch.select");
+      SelectInst *SelectValueInst = cast<SelectInst>(Builder.CreateSelect(
+          ValueCompare, ResultVector[1].first, DefaultResult, "switch.select"));
+      SelectValue = SelectValueInst;
+      if (HasBranchWeights) {
+        // We start with 3 probabilities, where the numerator is the
+        // corresponding BranchWeights[i], and the denominator is the sum over
+        // BranchWeights. We want the probability and negative probability of
+        // Condition == SecondCase.
+        assert(BranchWeights.size() == 3);
+        setBranchWeights(SelectValueInst, BranchWeights[2],
+                         BranchWeights[0] + BranchWeights[1],
+                         /*IsExpected=*/false);
+        }
     }
     Value *ValueCompare =
         Builder.CreateICmpEQ(Condition, FirstCase, "switch.selectcmp");
-    return Builder.CreateSelect(ValueCompare, ResultVector[0].first,
-                                SelectValue, "switch.select");
+    SelectInst *Ret = cast<SelectInst>(Builder.CreateSelect(
+        ValueCompare, ResultVector[0].first, SelectValue, "switch.select"));
+    if (HasBranchWeights) {
+      // We may have had a DefaultResult. Base the position of the first and
+      // second's branch weights accordingly. Also the proability that Condition
+      // != FirstCase needs to take that into account.
+      assert(BranchWeights.size() >= 2);
+      size_t FirstCasePos = (Condition != nullptr);
+      size_t SecondCasePos = FirstCasePos + 1;
+      uint32_t DefaultCase = (Condition != nullptr) ? BranchWeights[0] : 0;
+      setBranchWeights(Ret, BranchWeights[FirstCasePos],
+                       DefaultCase + BranchWeights[SecondCasePos],
+                       /*IsExpected=*/false);
+    }
+    return Ret;
   }
 
   // Handle the degenerate case where two cases have the same result value.
@@ -6379,8 +6411,16 @@ static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
           Value *And = Builder.CreateAnd(Condition, AndMask);
           Value *Cmp = Builder.CreateICmpEQ(
               And, Constant::getIntegerValue(And->getType(), AndMask));
-          return Builder.CreateSelect(Cmp, ResultVector[0].first,
-                                      DefaultResult);
+          SelectInst *Ret = cast<SelectInst>(Builder.CreateSelect(Cmp, ResultVector[0].first,
+                                      DefaultResult));
+          if (HasBranchWeights) {
+            // We know there's a Default case. We base the resulting branch
+            // weights off its probability.
+            assert(BranchWeights.size() >= 2);
+            setBranchWeights(Ret, accumulate(drop_begin(BranchWeights), 0),
+                             BranchWeights[0], /*IsExpected=*/false);
+          }
+          return Ret;
         }
       }
 
@@ -6397,7 +6437,14 @@ static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
         Value *And = Builder.CreateAnd(Condition, ~BitMask, "switch.and");
         Value *Cmp = Builder.CreateICmpEQ(
             And, Constant::getNullValue(And->getType()), "switch.selectcmp");
-        return Builder.CreateSelect(Cmp, ResultVector[0].first, DefaultResult);
+        SelectInst *Ret = cast<SelectInst>(
+            Builder.CreateSelect(Cmp, ResultVector[0].first, DefaultResult));
+        if (HasBranchWeights) {
+          assert(BranchWeights.size() >= 2);
+          setBranchWeights(Ret, accumulate(drop_begin(BranchWeights), 0),
+                           BranchWeights[0], /*IsExpected=*/false);
+        }
+        return Ret;
       }
     }
 
@@ -6408,7 +6455,14 @@ static Value *foldSwitchToSelect(const SwitchCaseResultVectorTy &ResultVector,
       Value *Cmp2 = Builder.CreateICmpEQ(Condition, CaseValues[1],
                                          "switch.selectcmp.case2");
       Value *Cmp = Builder.CreateOr(Cmp1, Cmp2, "switch.selectcmp");
-      return Builder.CreateSelect(Cmp, ResultVector[0].first, DefaultResult);
+      SelectInst *Ret = cast<SelectInst>(
+          Builder.CreateSelect(Cmp, ResultVector[0].first, DefaultResult));
+      if (HasBranchWeights) {
+        assert(BranchWeights.size() >= 2);
+        setBranchWeights(Ret, accumulate(drop_begin(BranchWeights), 0),
+                         BranchWeights[0], /*IsExpected=*/false);
+      }
+      return Ret;
     }
   }
 
@@ -6469,8 +6523,18 @@ static bool trySwitchToSelect(SwitchInst *SI, IRBuilder<> &Builder,
 
   assert(PHI != nullptr && "PHI for value select not found");
   Builder.SetInsertPoint(SI);
-  Value *SelectValue =
-      foldSwitchToSelect(UniqueResults, DefaultResult, Cond, Builder, DL);
+  SmallVector<uint32_t, 4> BranchWeights;
+  if (!ProfcheckDisableMetadataFixes) {
+    [[maybe_unused]] auto HasWeights =
+        extractBranchWeights(getBranchWeightMDNode(*SI), BranchWeights);
+    assert(!HasWeights == (BranchWeights.empty()));
+  }
+  assert(BranchWeights.empty() ||
+         (BranchWeights.size() >=
+          UniqueResults.size() + (DefaultResult != nullptr)));
+
+  Value *SelectValue = foldSwitchToSelect(UniqueResults, DefaultResult, Cond,
+                                          Builder, DL, BranchWeights);
   if (!SelectValue)
     return false;
 
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll b/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
index fe2e897125eb8..e0e00c1154059 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
@@ -1,5 +1,5 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals
+; RUN: opt < %s -passes=prof-inject,simplifycfg -profcheck-weights-for-test -simplifycfg-require-and-preserve-domtree=1 -S | FileCheck %s
 
 ; int foo1_with_default(int a) {
 ;   switch(a) {
@@ -15,9 +15,9 @@ define i32 @foo1_with_default(i32 %a) {
 ; CHECK-LABEL: @foo1_with_default(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = icmp eq i32 [[A:%.*]], 20
-; CHECK-NEXT:    [[SWITCH_SELECT:%.*]] = select i1 [[SWITCH_SELECTCMP]], i32 2, i32 4
+; CHECK-NEXT:    [[SWITCH_SELECT:%.*]] = select i1 [[SWITCH_SELECTCMP]], i32 2, i32 4, !prof [[PROF1:![0-9]+]]
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP1:%.*]] = icmp eq i32 [[A]], 10
-; CHECK-NEXT:    [[SWITCH_SELECT2:%.*]] = select i1 [[SWITCH_SELECTCMP1]], i32 10, i32 [[SWITCH_SELECT]]
+; CHECK-NEXT:    [[SWITCH_SELECT2:%.*]] = select i1 [[SWITCH_SELECTCMP1]], i32 10, i32 [[SWITCH_SELECT]], !prof [[PROF2:![0-9]+]]
 ; CHECK-NEXT:    ret i32 [[SWITCH_SELECT2]]
 ;
 entry:
@@ -47,7 +47,7 @@ define i32 @same_value(i32 %a) {
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP_CASE1:%.*]] = icmp eq i32 [[A:%.*]], 10
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP_CASE2:%.*]] = icmp eq i32 [[A]], 20
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = or i1 [[SWITCH_SELECTCMP_CASE1]], [[SWITCH_SELECTCMP_CASE2]]
-; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i32 10, i32 4
+; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i32 10, i32 4, !prof [[PROF3:![0-9]+]]
 ; CHECK-NEXT:    ret i32 [[TMP0]]
 ;
 entry:
@@ -71,7 +71,7 @@ define i1 @switch_to_select_same2_case_results_different_default(i8 %0) {
 ; CHECK-LABEL: @switch_to_select_same2_case_results_different_default(
 ; CHECK-NEXT:    [[SWITCH_AND:%.*]] = and i8 [[TMP0:%.*]], -5
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = icmp eq i8 [[SWITCH_AND]], 0
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false, !prof [[PROF3]]
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   switch i8 %0, label %2 [
@@ -92,7 +92,7 @@ define i1 @switch_to_select_same2_case_results_different_default_and_positive_of
 ; CHECK-NEXT:    [[TMP2:%.*]] = sub i8 [[TMP0:%.*]], 43
 ; CHECK-NEXT:    [[SWITCH_AND:%.*]] = and i8 [[TMP2]], -3
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = icmp eq i8 [[SWITCH_AND]], 0
-; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false, !prof [[PROF3]]
 ; CHECK-NEXT:    ret i1 [[TMP3]]
 ;
   switch i8 %0, label %2 [
@@ -114,7 +114,7 @@ define i8 @switch_to_select_same2_case_results_different_default_and_negative_of
 ; CHECK-NEXT:    [[TMP0:%.*]] = sub i32 [[I:%.*]], -5
 ; CHECK-NEXT:    [[SWITCH_AND:%.*]] = and i32 [[TMP0]], -3
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = icmp eq i32 [[SWITCH_AND]], 0
-; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i8 3, i8 42
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i8 3, i8 42, !prof [[PROF3]]
 ; CHECK-NEXT:    ret i8 [[TMP1]]
 ;
 entry:
@@ -136,7 +136,7 @@ define i1 @switch_to_select_same4_case_results_different_default(i32 %i) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[SWITCH_AND:%.*]] = and i32 [[I:%.*]], -7
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = icmp eq i32 [[SWITCH_AND]], 0
-; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false, !prof [[PROF4:![0-9]+]]
 ; CHECK-NEXT:    ret i1 [[TMP0]]
 ;
 entry:
@@ -160,7 +160,7 @@ define i1 @switch_to_select_same4_case_results_different_default_alt_bitmask(i32
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[SWITCH_AND:%.*]] = and i32 [[I:%.*]], -11
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = icmp eq i32 [[SWITCH_AND]], 0
-; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false, !prof [[PROF4]]
 ; CHECK-NEXT:    ret i1 [[TMP0]]
 ;
 entry:
@@ -185,7 +185,7 @@ define i1 @switch_to_select_same4_case_results_different_default_positive_offset
 ; CHECK-NEXT:    [[TMP0:%.*]] = sub i32 [[I:%.*]], 2
 ; CHECK-NEXT:    [[SWITCH_AND:%.*]] = and i32 [[TMP0]], -11
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = icmp eq i32 [[SWITCH_AND]], 0
-; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false, !prof [[PROF4]]
 ; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
 entry:
@@ -212,7 +212,7 @@ define i1 @switch_to_select_invalid_mask(i32 %i) {
 ; CHECK-NEXT:      i32 4, label [[LOR_END]]
 ; CHECK-NEXT:      i32 10, label [[LOR_END]]
 ; CHECK-NEXT:      i32 12, label [[LOR_END]]
-; CHECK-NEXT:    ]
+; CHECK-NEXT:    ], !prof [[PROF5:![0-9]+]]
 ; CHECK:       lor.rhs:
 ; CHECK-NEXT:    br label [[LOR_END]]
 ; CHECK:       lor.end:
@@ -242,7 +242,7 @@ define i1 @switch_to_select_nonpow2_cases(i32 %i) {
 ; CHECK-NEXT:      i32 0, label [[LOR_END:%.*]]
 ; CHECK-NEXT:      i32 2, label [[LOR_END]]
 ; CHECK-NEXT:      i32 4, label [[LOR_END]]
-; CHECK-NEXT:    ]
+; CHECK-NEXT:    ], !prof [[PROF6:![0-9]+]]
 ; CHECK:       lor.rhs:
 ; CHECK-NEXT:    br label [[LOR_END]]
 ; CHECK:       lor.end:
@@ -273,7 +273,7 @@ define i8 @switch_to_select_two_case_results_no_default(i32 %i) {
 ; CHECK-NEXT:      i32 2, label [[END]]
 ; CHECK-NEXT:      i32 4, label [[CASE3:%.*]]
 ; CHECK-NEXT:      i32 6, label [[CASE3]]
-; CHECK-NEXT:    ]
+; CHECK-NEXT:    ], !prof [[PROF5]]
 ; CHECK:       case3:
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       default:
@@ -315,7 +315,7 @@ define i1 @no_range(i8 %f) {
 ; CHECK-NEXT:  bb3:
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[F:%.*]], 60
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 60
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false, !prof [[PROF7:![0-9]+]]
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   switch i8 %f, label %bb1 [
@@ -364,7 +364,7 @@ define i1 @negative_no_range(i8 %f) {
 ; CHECK-NEXT:      i8 -3, label [[BB2]]
 ; CHECK-NEXT:      i8 -2, label [[BB2]]
 ; CHECK-NEXT:      i8 -1, label [[BB2]]
-; CHECK-NEXT:    ]
+; CHECK-NEXT:    ], !prof [[PROF8:![0-9]+]]
 ; CHECK:       bb2:
 ; CHECK-NEXT:    br label [[BB3]]
 ; CHECK:       bb3:
@@ -405,7 +405,7 @@ define i1 @range0to4odd(i8 range(i8 0, 4) %f) {
 ; CHECK-NEXT:  bb3:
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[F:%.*]], 1
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 1
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false, !prof [[PROF3]]
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   switch i8 %f, label %bb1 [
@@ -426,7 +426,7 @@ define i1 @range1to4odd(i8 range(i8 1, 4) %f) {
 ; CHECK-NEXT:  bb3:
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[F:%.*]], 1
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 1
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false, !prof [[PROF3]]
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   switch i8 %f, label %bb1 [
@@ -447,7 +447,7 @@ define i1 @range0to8odd(i8 range(i8 0, 8) %f) {
 ; CHECK-NEXT:  bb3:
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[F:%.*]], 1
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 1
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false, !prof [[PROF4]]
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   switch i8 %f, label %bb1 [
@@ -470,7 +470,7 @@ define i1 @range0to8most_significant_bit(i8 range(i8 0, 8) %f) {
 ; CHECK-NEXT:  bb3:
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[F:%.*]], 4
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 4
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false, !prof [[PROF4]]
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   switch i8 %f, label %bb1 [
@@ -493,7 +493,7 @@ define i1 @range0to15_middle_two_bits(i8 range(i8 0, 16) %f) {
 ; CHECK-NEXT:  bb3:
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[F:%.*]], 6
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 6
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false, !prof [[PROF4]]
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   switch i8 %f, label %bb1 [
@@ -517,7 +517,7 @@ define i1 @negative_range0to15(i8 range(i8 0, 16) %f) {
 ; CHECK-NEXT:      i8 6, label [[BB2:%.*]]
 ; CHECK-NEXT:      i8 7, label [[BB2]]
 ; CHECK-NEXT:      i8 14, label [[BB2]]
-; CHECK-NEXT:    ]
+; CHECK-NEXT:    ], !prof [[PROF6]]
 ; CHECK:       bb2:
 ; CHECK-NEXT:    br label [[BB3]]
 ; CHECK:       bb3:
@@ -544,7 +544,7 @@ define i1 @negative_range0to15_pow_2(i8 range(i8 0, 16) %f) {
 ; CHECK-NEXT:    [[TMP0:%.*]] = sub i8 [[F:%.*]], 6
 ; CHECK-NEXT:    [[SWITCH_AND:%.*]] = and i8 [[TMP0]], -2
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = icmp eq i8 [[SWITCH_AND]], 0
-; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false, !prof [[PROF3]]
 ; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   switch i8 %f, label %bb1 [
@@ -566,7 +566,7 @@ define i1 @negative_range0to5even(i8 range(i8 0, 5) %f) {
 ; CHECK-NEXT:    [[TMP0:%.*]] = sub i8 [[F:%.*]], 2
 ; CHECK-NEXT:    [[SWITCH_AND:%.*]] = and i8 [[TMP0]], -3
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = icmp eq i8 [[SWITCH_AND]], 0
-; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false, !prof [[PROF3]]
 ; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   switch i8 %f, label %bb1 [
@@ -586,7 +586,7 @@ define i1 @range0to15_corner_case(i8 range(i8 0, 16) %f) {
 ; CHECK-LABEL: @range0to15_corner_case(
 ; CHECK-NEXT:  bb3:
 ; CHECK-NEXT:    [[COND:%.*]] = icmp eq i8 [[F:%.*]], 15
-; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[COND]], i1 true, i1 false
+; CHECK-NEXT:    [[DOT:%.*]] = select i1 [[COND]], i1 true, i1 false, !prof [[PROF9:![0-9]+]]
 ; CHECK-NEXT:    ret i1 [[DOT]]
 ;
   switch i8 %f, label %bb1 [
@@ -607,7 +607,7 @@ define i1 @negative_range0to15_corner_case(i8 range(i8 0, 16) %f) {
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP_CASE1:%.*]] = icmp eq i8 [[F:%.*]], 15
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP_CASE2:%.*]] = icmp eq i8 [[F]], 8
 ; CHECK-NEXT:    [[SWITCH_SELECTCMP:%.*]] = or i1 [[SWITCH_SELECTCMP_CASE1]], [[SWITCH_SELECTCMP_CASE2]]
-; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[SWITCH_SELECTCMP]], i1 true, i1 false, !prof [[PROF3]]
 ; CHECK-NEXT:    ret i1 [[TMP0]]
 ;
   switch i8 %f, label %bb1 [
@@ -631,7 +631,7 @@ define i1 @range0to15_out_of_range_non_prime(i8 range(i8 0, 16) %f) {
 ; CHECK-NEXT:  bb3:
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[F:%.*]], 6
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 6
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false, !prof [[PROF4]]
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   switch i8 %f, label %bb1 [
@@ -655,7 +655,7 @@ define i1 @range0to15_out_of_range_non_prime_more(i8 range(i8 0, 16) %f) {
 ; CHECK-NEXT:  bb3:
 ; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[F:%.*]], 6
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i8 [[TMP0]], 6
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i1 true, i1 false, !prof [[PROF4]]
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   switch i8 %f, label %bb1 [
@@ -681,7 +681,7 @@ define i1 @negative_range0to15_out_of_range_non_prime(i8 range(i8 0, 16) %f) {
 ; CHECK-NEXT:      i8 6, label [[BB2:%.*]]
 ; CHECK-NEXT:      i8 14, label [[BB2]]
 ; CHECK-NEXT:      i8 15, label [[BB2]]
-; CHECK-NEXT:    ]
+; CHECK-NEXT:    ], !prof [[PROF6]]
 ; CHECK:       bb2:
 ; CHECK-NEXT:    br label [[BB3]]
 ; CHECK:       bb3:
@@ -709,7 +709,7 @@ define i1 @negative_range0to15_out_of_range(i8 range(i8 0, 16) %f) {
 ; CHECK-NEXT:      i8 6, label [[BB2:%.*]]
 ; CHECK-NEXT: ...
[truncated]

llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll

alanzhao1

In general this patch LGTM.

I noticed that one downside of using -profcheck-weights-for-test is that the original branch weights aren't in the test, so it's hard for me to understand how this change modifies the branch weights.

mtrofin · 2025-09-24T15:15:05Z

In general this patch LGTM.

I noticed that one downside of using -profcheck-weights-for-test is that the original branch weights aren't in the test, so it's hard for me to understand how this change modifies the branch weights.

You're right. I think I'll just use -profcheck-weights-for-test "offline" to generate the .ll that is checked in. It's a convenience anyway - to avoid one having to write interesting profile metadata by hand in large tests. wdyt?

mtrofin · 2025-09-26T21:15:13Z

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Sep 26, 9:16 PM UTC: @mtrofin merged this pull request with Graphite.

…lvm#159645) Propagate `!prof` from `switch` instructions. Issue llvm#147390

mtrofin mentioned this pull request Sep 18, 2025

[profcheck] Option to inject distinct small weights #159644

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llvmbot added the llvm:transforms label Sep 18, 2025

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mtrofin force-pushed the users/mtrofin/09-15-_profcheck_simplifycfg_propagate_prof_from_switch_to_select_ branch from 92728fa to 6d3342f Compare September 18, 2025 20:19

mtrofin commented Sep 18, 2025

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mtrofin force-pushed the users/mtrofin/09-15-_profcheck_simplifycfg_propagate_prof_from_switch_to_select_ branch from 6d3342f to 8027f03 Compare September 24, 2025 15:13

mtrofin force-pushed the users/mtrofin/09-18-_profcheck_option_to_inject_distinct_small_weights branch from c42de45 to 518490e Compare September 24, 2025 15:13

Base automatically changed from users/mtrofin/09-18-_profcheck_option_to_inject_distinct_small_weights to main September 24, 2025 18:40

mtrofin force-pushed the users/mtrofin/09-15-_profcheck_simplifycfg_propagate_prof_from_switch_to_select_ branch 3 times, most recently from bb09459 to a0452c3 Compare September 24, 2025 20:16

mtrofin requested a review from alanzhao1 September 24, 2025 20:18

mtrofin force-pushed the users/mtrofin/09-15-_profcheck_simplifycfg_propagate_prof_from_switch_to_select_ branch from a0452c3 to e277ce0 Compare September 25, 2025 00:31

[profcheck][SimplifyCFG] Propagate !prof from switch to select

d9ac85c

mtrofin force-pushed the users/mtrofin/09-15-_profcheck_simplifycfg_propagate_prof_from_switch_to_select_ branch from e277ce0 to d9ac85c Compare September 25, 2025 00:34

mtrofin mentioned this pull request Sep 25, 2025

[SimplifyCFG][PGO] Reuse existing setBranchWeights #160629

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alanzhao1 approved these changes Sep 26, 2025

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mtrofin merged commit d2f14bc into main Sep 26, 2025
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mtrofin deleted the users/mtrofin/09-15-_profcheck_simplifycfg_propagate_prof_from_switch_to_select_ branch September 26, 2025 21:16

antoniofrighetto mentioned this pull request Sep 29, 2025

clang crashes at -O1 and above on x86_64-linux-gnu: Assertion `isa<To>(Val) && "cast<Ty>() argument of incompatible type!"' failed #161137

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mtrofin mentioned this pull request Oct 1, 2025

[SimplifyCFG][profcheck] Synthesize profile for br (X == 0 | X == 1), T, F1 -> switch #161549

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This was referenced Oct 2, 2025

[SimplifyCFG][profcheck] Handle branch weights in simplifySwitchLookup #161739

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[SimplifyCFG][profcheck] Profile propagation for indirectbr #161747

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mahesh-attarde pushed a commit to mahesh-attarde/llvm-project that referenced this pull request Oct 3, 2025

[profcheck][SimplifyCFG] Propagate !prof from switch to select (l…

648e3b9

…lvm#159645) Propagate `!prof` from `switch` instructions. Issue llvm#147390

mtrofin mentioned this pull request Oct 4, 2025

[profcheck] Update exclusion list to reflect fixes #161943

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