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[llvm] Introduce MoveEntryAllocaInit pass #164882

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@nimit25 nimit25 commented Oct 23, 2025 •
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Fixes #150120

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llvmbot commented Oct 23, 2025

@llvm/pr-subscribers-llvm-transforms

Author: Nimit Sachdeva (nimit25)

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Full diff: https://github.com/llvm/llvm-project/pull/164882.diff

13 Files Affected:

  • (modified) llvm/include/llvm/Transforms/Utils/MoveAutoInit.h (+6)
  • (modified) llvm/lib/Passes/PassBuilderPipelines.cpp (+2)
  • (modified) llvm/lib/Passes/PassRegistry.def (+1)
  • (modified) llvm/lib/Transforms/Utils/MoveAutoInit.cpp (+24-3)
  • (modified) llvm/test/Other/new-pm-defaults.ll (+1)
  • (modified) llvm/test/Other/new-pm-lto-defaults.ll (+1)
  • (modified) llvm/test/Other/new-pm-thinlto-postlink-defaults.ll (+1)
  • (modified) llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll (+1)
  • (modified) llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll (+1)
  • (modified) llvm/test/Other/new-pm-thinlto-prelink-defaults.ll (+1)
  • (modified) llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll (+1)
  • (modified) llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll (+1)
  • (added) llvm/test/Transforms/MoveAutoInit/entry-alloca.ll (+50)
diff --git a/llvm/include/llvm/Transforms/Utils/MoveAutoInit.h b/llvm/include/llvm/Transforms/Utils/MoveAutoInit.h
index 980b55f46f114..e8565e6942bc2 100644
--- a/llvm/include/llvm/Transforms/Utils/MoveAutoInit.h
+++ b/llvm/include/llvm/Transforms/Utils/MoveAutoInit.h
@@ -24,6 +24,12 @@ class MoveAutoInitPass : public PassInfoMixin<MoveAutoInitPass> {
 public:
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 };
+
+/// Move entry block initializations of allocas closer to their guarded users.
+class MoveEntryAllocaInitPass : public PassInfoMixin<MoveEntryAllocaInitPass> {
+public:
+  PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
+};
 } // end namespace llvm
 
 #endif // LLVM_TRANSFORMS_UTILS_MOVEAUTOINIT_H
diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index bd03ac090721c..470bc0afa22d7 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -765,6 +765,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
 
   FPM.addPass(DSEPass());
   FPM.addPass(MoveAutoInitPass());
+  FPM.addPass(MoveEntryAllocaInitPass());
 
   FPM.addPass(createFunctionToLoopPassAdaptor(
       LICMPass(PTO.LicmMssaOptCap, PTO.LicmMssaNoAccForPromotionCap,
@@ -2140,6 +2141,7 @@ PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
   // Nuke dead stores.
   MainFPM.addPass(DSEPass());
   MainFPM.addPass(MoveAutoInitPass());
+  MainFPM.addPass(MoveEntryAllocaInitPass());
   MainFPM.addPass(MergedLoadStoreMotionPass());
 
   invokeVectorizerStartEPCallbacks(MainFPM, Level);
diff --git a/llvm/lib/Passes/PassRegistry.def b/llvm/lib/Passes/PassRegistry.def
index 1853cdd45d0ee..7950040cd3623 100644
--- a/llvm/lib/Passes/PassRegistry.def
+++ b/llvm/lib/Passes/PassRegistry.def
@@ -485,6 +485,7 @@ FUNCTION_PASS("memprof", MemProfilerPass())
 FUNCTION_PASS("mergeicmps", MergeICmpsPass())
 FUNCTION_PASS("mergereturn", UnifyFunctionExitNodesPass())
 FUNCTION_PASS("move-auto-init", MoveAutoInitPass())
+FUNCTION_PASS("move-entry-alloca-init", MoveEntryAllocaInitPass())
 FUNCTION_PASS("nary-reassociate", NaryReassociatePass())
 FUNCTION_PASS("newgvn", NewGVNPass())
 FUNCTION_PASS("no-op-function", NoOpFunctionPass())
diff --git a/llvm/lib/Transforms/Utils/MoveAutoInit.cpp b/llvm/lib/Transforms/Utils/MoveAutoInit.cpp
index ad105f5a57b49..b9993dfe56577 100644
--- a/llvm/lib/Transforms/Utils/MoveAutoInit.cpp
+++ b/llvm/lib/Transforms/Utils/MoveAutoInit.cpp
@@ -101,7 +101,9 @@ static BasicBlock *usersDominator(const MemoryLocation &ML, Instruction *I,
   return CurrentDominator;
 }
 
-static bool runMoveAutoInit(Function &F, DominatorTree &DT, MemorySSA &MSSA) {
+static bool runMoveAutoInit(
+    Function &F, DominatorTree &DT, MemorySSA &MSSA,
+    function_ref<bool(const Instruction &)> ShouldProcess) {
   BasicBlock &EntryBB = F.getEntryBlock();
   SmallVector<std::pair<Instruction *, BasicBlock *>> JobList;
 
@@ -109,7 +111,7 @@ static bool runMoveAutoInit(Function &F, DominatorTree &DT, MemorySSA &MSSA) {
   // Compute movable instructions.
   //
   for (Instruction &I : EntryBB) {
-    if (!hasAutoInitMetadata(I))
+    if (!ShouldProcess(I))
       continue;
 
     std::optional<MemoryLocation> ML = writeToAlloca(I);
@@ -221,7 +223,26 @@ PreservedAnalyses MoveAutoInitPass::run(Function &F,
 
   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
   auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
-  if (!runMoveAutoInit(F, DT, MSSA))
+  auto ShouldProcess = [](const Instruction &I) -> bool {
+    return hasAutoInitMetadata(I);
+  };
+  if (!runMoveAutoInit(F, DT, MSSA, ShouldProcess))
+    return PreservedAnalyses::all();
+
+  PreservedAnalyses PA;
+  PA.preserve<DominatorTreeAnalysis>();
+  PA.preserve<MemorySSAAnalysis>();
+  PA.preserveSet<CFGAnalyses>();
+  return PA;
+}
+
+PreservedAnalyses MoveEntryAllocaInitPass::run(Function &F,
+                                               FunctionAnalysisManager &AM) {
+
+  auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
+  auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
+  auto ShouldProcess = [](const Instruction &) { return true; };
+  if (!runMoveAutoInit(F, DT, MSSA, ShouldProcess))
     return PreservedAnalyses::all();
 
   PreservedAnalyses PA;
diff --git a/llvm/test/Other/new-pm-defaults.ll b/llvm/test/Other/new-pm-defaults.ll
index 65b96c8b8ef5d..0bc59cbffa594 100644
--- a/llvm/test/Other/new-pm-defaults.ll
+++ b/llvm/test/Other/new-pm-defaults.ll
@@ -218,6 +218,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass
 ; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
+; CHECK-O23SZ-NEXT: Running pass: MoveEntryAllocaInitPass on foo
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
diff --git a/llvm/test/Other/new-pm-lto-defaults.ll b/llvm/test/Other/new-pm-lto-defaults.ll
index f595dfe1d6845..4ce7a968fe3b2 100644
--- a/llvm/test/Other/new-pm-lto-defaults.ll
+++ b/llvm/test/Other/new-pm-lto-defaults.ll
@@ -118,6 +118,7 @@
 ; CHECK-O23SZ-NEXT: Running analysis: PostDominatorTreeAnalysis on foo
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass on foo
 ; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
+; CHECK-O23SZ-NEXT: Running pass: MoveEntryAllocaInitPass on foo
 ; CHECK-O23SZ-NEXT: Running pass: MergedLoadStoreMotionPass on foo
 ; CHECK-EP-VECTORIZER-START-NEXT: Running pass: NoOpFunctionPass on foo
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass on foo
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
index 3a0fffe426da1..6f94522401396 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
@@ -143,6 +143,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass
 ; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
+; CHECK-O23SZ-NEXT: Running pass: MoveEntryAllocaInitPass on foo
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass on loop
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
index 4623edcaf6656..05321565e2c2d 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
@@ -127,6 +127,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass
 ; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
+; CHECK-O23SZ-NEXT: Running pass: MoveEntryAllocaInitPass on foo
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
index 590afd925e841..c0a6b3851b376 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
@@ -136,6 +136,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass
 ; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass
+; CHECK-O23SZ-NEXT: Running pass: MoveEntryAllocaInitPass
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
diff --git a/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll b/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
index dd6acd2c51ee7..280f36749850c 100644
--- a/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
@@ -175,6 +175,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass
 ; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass
+; CHECK-O23SZ-NEXT: Running pass: MoveEntryAllocaInitPass
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass on loop
diff --git a/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
index ee054527e20bd..b719045f890a4 100644
--- a/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
@@ -176,6 +176,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass
 ; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
+; CHECK-O23SZ-NEXT: Running pass: MoveEntryAllocaInitPass on foo
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
diff --git a/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
index fd95e94f3c8b9..3d73e3ca2c2b7 100644
--- a/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
@@ -140,6 +140,7 @@
 ; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
 ; CHECK-O23SZ-NEXT: Running pass: DSEPass
 ; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
+; CHECK-O23SZ-NEXT: Running pass: MoveEntryAllocaInitPass on foo
 ; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
 ; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
 ; CHECK-O23SZ-NEXT: Running pass: LICMPass
diff --git a/llvm/test/Transforms/MoveAutoInit/entry-alloca.ll b/llvm/test/Transforms/MoveAutoInit/entry-alloca.ll
new file mode 100644
index 0000000000000..31906551e60fc
--- /dev/null
+++ b/llvm/test/Transforms/MoveAutoInit/entry-alloca.ll
@@ -0,0 +1,50 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt -passes='move-entry-alloca-init' -verify-memoryssa -S < %s | FileCheck %s
+
+declare void @bar(ptr)
+
+define void @src(i32 %a, i32 %b) {
+; CHECK-LABEL: define void @src(
+; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:    [[A_ADDR:%.*]] = alloca i32
+; CHECK-NEXT:    [[B_ADDR:%.*]] = alloca i32
+; CHECK-NEXT:    [[S_ADDR:%.*]] = alloca { ptr, ptr }
+; CHECK:         [[S_X:%.*]] = getelementptr inbounds { ptr, ptr }, ptr [[S_ADDR]], i32 0, i32 0
+; CHECK:         [[S_Y:%.*]] = getelementptr inbounds { ptr, ptr }, ptr [[S_ADDR]], i32 0, i32 1
+; CHECK:         [[CMP:%.*]] = icmp slt i32 [[A]], [[B]]
+; CHECK:         br i1 [[CMP]], label [[COLD:%.*]], label [[RET:%.*]]
+;
+; CHECK:       cold:
+; CHECK-NEXT:    store i32 [[A]], ptr [[A_ADDR]], align 4
+; CHECK-NEXT:    store i32 [[B]], ptr [[B_ADDR]], align 4
+; CHECK-NEXT:    store ptr [[A_ADDR]], ptr [[S_X]], align 8
+; CHECK-NEXT:    store ptr [[B_ADDR]], ptr [[S_Y]], align 8
+; CHECK-NEXT:    call void @bar(ptr [[S_ADDR]])
+; CHECK-NEXT:    br label [[RET]]
+;
+; CHECK:       ret:
+; CHECK-NEXT:    ret void
+;
+  %a.addr = alloca i32
+  %b.addr = alloca i32
+  %s.addr = alloca { ptr, ptr }
+
+  store i32 %a, ptr %a.addr
+  store i32 %b, ptr %b.addr
+
+  %s.x = getelementptr inbounds { ptr, ptr }, ptr %s.addr, i32 0, i32 0
+  store ptr %a.addr, ptr %s.x
+
+  %s.y = getelementptr inbounds { ptr, ptr }, ptr %s.addr, i32 0, i32 1
+  store ptr %b.addr, ptr %s.y
+
+  %cmp = icmp slt i32 %a, %b
+  br i1 %cmp, label %cold, label %ret
+
+cold:
+  call void @bar(ptr %s.addr)
+  br label %ret
+
+ret:
+  ret void
+}

@nimit25 nimit25 changed the title #150120 Introduce MoveEntryAllocaInit pass [Transform] Introduce MoveEntryAllocaInit pass Oct 23, 2025
@nimit25 nimit25 changed the title [Transform] Introduce MoveEntryAllocaInit pass [llvm] Introduce MoveEntryAllocaInit pass Oct 23, 2025
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github-actions bot commented Oct 23, 2025 •
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✅ With the latest revision this PR passed the C/C++ code formatter.

nikic
nikic reviewed Oct 23, 2025
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Why is this a new pass that runs after MoveAutoInit and does exactly the same thing just not limited to auto-init allocas? Wouldn't it make more sense to have a single pass for this (that handles both auto-init and non-auto-init)?

@nimit25
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nimit25 commented Oct 24, 2025 •
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Why is this a new pass that runs after MoveAutoInit and does exactly the same thing just not limited to auto-init allocas? Wouldn't it make more sense to have a single pass for this (that handles both auto-init and non-auto-init)?

Will move the new pass's logic into MoveAutoInit to be run after auto-init

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Missed optimization: Lowering struct materialization into cold branches

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