[llvm] llvm-reduce: Do not reduce alloca array sizes to 0 (PR #132864)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm updated https://github.com/llvm/llvm-project/pull/132864

>From c2e2461a15007f748688ee895865b3e10d85cfc2 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Tue, 25 Mar 2025 09:39:18 +0700
Subject: [PATCH] llvm-reduce: Do not reduce alloca array sizes to 0

Fixes #64340
---
 .../llvm-reduce/reduce-operands-alloca.ll     | 69 +++++++++++++++++++
 .../llvm-reduce/deltas/ReduceOperands.cpp     |  5 ++
 2 files changed, 74 insertions(+)
 create mode 100644 llvm/test/tools/llvm-reduce/reduce-operands-alloca.ll

diff --git a/llvm/test/tools/llvm-reduce/reduce-operands-alloca.ll b/llvm/test/tools/llvm-reduce/reduce-operands-alloca.ll
new file mode 100644
index 0000000000000..61c46185b3378
--- /dev/null
+++ b/llvm/test/tools/llvm-reduce/reduce-operands-alloca.ll
@@ -0,0 +1,69 @@
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=operands-zero --test FileCheck --test-arg --check-prefix=CHECK --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck %s --check-prefixes=CHECK,ZERO < %t
+
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=operands-one --test FileCheck --test-arg --check-prefix=CHECK --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck %s --check-prefixes=CHECK,ONE < %t
+
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=operands-poison --test FileCheck --test-arg --check-prefix=CHECK --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck %s --check-prefixes=CHECK,POISON < %t
+
+
+; CHECK-LABEL: @dyn_alloca(
+; ZERO: %alloca = alloca i32, i32 %size, align 4
+; ONE: %alloca = alloca i32, align 4
+; POISON: %alloca = alloca i32, i32 %size, align 4
+define void @dyn_alloca(i32 %size) {
+ %alloca = alloca i32, i32 %size
+ store i32 0, ptr %alloca
+ ret void
+}
+
+; CHECK-LABEL: @alloca_0_elt(
+; ZERO: %alloca = alloca i32, i32 0, align 4
+; ONE: %alloca = alloca i32, i32 0, align 4
+; POISON:  %alloca = alloca i32, i32 0, align 4
+define void @alloca_0_elt() {
+ %alloca = alloca i32, i32 0
+ store i32 0, ptr %alloca
+ ret void
+}
+
+; CHECK-LABEL: @alloca_1_elt(
+; ZERO: %alloca = alloca i32, align 4
+; ONE: %alloca = alloca i32, align 4
+; POISON: %alloca = alloca i32, align 4
+define void @alloca_1_elt() {
+ %alloca = alloca i32, i32 1
+ store i32 0, ptr %alloca
+ ret void
+}
+
+; CHECK-LABEL: @alloca_1024_elt(
+; ZERO: %alloca = alloca i32, i32 1024, align 4
+; ONE: %alloca = alloca i32, align 4
+; POISON: %alloca = alloca i32, i32 1024, align 4
+define void @alloca_1024_elt() {
+ %alloca = alloca i32, i32 1024
+ store i32 0, ptr %alloca
+ ret void
+}
+
+; CHECK-LABEL: @alloca_poison_elt(
+; ZERO: %alloca = alloca i32, i32 poison, align 4
+; ONE: %alloca = alloca i32, align 4
+; POISON: %alloca = alloca i32, i32 poison, align 4
+define void @alloca_poison_elt() {
+ %alloca = alloca i32, i32 poison
+ store i32 0, ptr %alloca
+ ret void
+}
+
+; CHECK-LABEL: @alloca_constexpr_elt(
+; ZERO: %alloca = alloca i32, i32 ptrtoint (ptr @alloca_constexpr_elt to i32)
+; ONE: %alloca = alloca i32, align 4
+; POISON: %alloca = alloca i32, i32 ptrtoint (ptr @alloca_constexpr_elt to i32)
+define void @alloca_constexpr_elt() {
+ %alloca = alloca i32, i32 ptrtoint (ptr @alloca_constexpr_elt to i32)
+ store i32 0, ptr %alloca
+ ret void
+}
diff --git a/llvm/tools/llvm-reduce/deltas/ReduceOperands.cpp b/llvm/tools/llvm-reduce/deltas/ReduceOperands.cpp
index a4fdd9ce8033b..b0bca015434fa 100644
--- a/llvm/tools/llvm-reduce/deltas/ReduceOperands.cpp
+++ b/llvm/tools/llvm-reduce/deltas/ReduceOperands.cpp
@@ -125,6 +125,11 @@ void llvm::reduceOperandsZeroDeltaPass(Oracle &O, ReducerWorkItem &WorkItem) {
   auto ReduceValue = [](Use &Op) -> Value * {
     if (!shouldReduceOperand(Op))
       return nullptr;
+
+    // Avoid introducing 0-sized allocations.
+    if (isa<AllocaInst>(Op.getUser()))
+      return nullptr;
+
     // Don't duplicate an existing switch case.
     if (auto *IntTy = dyn_cast<IntegerType>(Op->getType()))
       if (switchCaseExists(Op, ConstantInt::get(IntTy, 0)))