[llvm] [DSE] Fold small malloc + zero-store into calloc (PR #106069)
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Mon Aug 26 06:13:20 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Pedro Lobo (pedroclobo)
<details>
<summary>Changes</summary>
---
Full diff: https://github.com/llvm/llvm-project/pull/106069.diff
3 Files Affected:
- (modified) llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp (+34-12)
- (modified) llvm/test/Transforms/DeadStoreElimination/noop-stores.ll (+10)
- (modified) llvm/test/Transforms/DeadStoreElimination/simple.ll (+4-6)
``````````diff
diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 992139a95a43d3..4d271030764d3b 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -1849,10 +1849,12 @@ struct DSEState {
bool tryFoldIntoCalloc(MemoryDef *Def, const Value *DefUO) {
Instruction *DefI = Def->getMemoryInst();
MemSetInst *MemSet = dyn_cast<MemSetInst>(DefI);
- if (!MemSet)
- // TODO: Could handle zero store to small allocation as well.
+ StoreInst *Store = dyn_cast<StoreInst>(DefI);
+ if (!MemSet && !Store)
return false;
- Constant *StoredConstant = dyn_cast<Constant>(MemSet->getValue());
+ Constant *StoredConstant =
+ MemSet ? dyn_cast<Constant>(MemSet->getValue())
+ : dyn_cast<Constant>(Store->getValueOperand());
if (!StoredConstant || !StoredConstant->isNullValue())
return false;
@@ -1880,14 +1882,16 @@ struct DSEState {
if (!MallocDef)
return false;
- auto shouldCreateCalloc = [](CallInst *Malloc, CallInst *Memset) {
+ auto shouldCreateCalloc = [](CallInst *Malloc, Instruction *MI) {
// Check for br(icmp ptr, null), truebb, falsebb) pattern at the end
// of malloc block
auto *MallocBB = Malloc->getParent(),
- *MemsetBB = Memset->getParent();
+ *MemsetBB = MI->getParent();
if (MallocBB == MemsetBB)
return true;
- auto *Ptr = Memset->getArgOperand(0);
+ auto *Ptr = dyn_cast<CallInst>(MI)
+ ? dyn_cast<CallInst>(MI)->getArgOperand(0)
+ : dyn_cast<StoreInst>(MI)->getPointerOperand();
auto *TI = MallocBB->getTerminator();
BasicBlock *TrueBB, *FalseBB;
if (!match(TI, m_Br(m_SpecificICmp(ICmpInst::ICMP_EQ, m_Specific(Ptr),
@@ -1899,12 +1903,30 @@ struct DSEState {
return true;
};
- if (Malloc->getOperand(0) != MemSet->getLength())
- return false;
- if (!shouldCreateCalloc(Malloc, MemSet) ||
- !DT.dominates(Malloc, MemSet) ||
- !memoryIsNotModifiedBetween(Malloc, MemSet, BatchAA, DL, &DT))
- return false;
+ if (MemSet) {
+ if (Malloc->getOperand(0) != MemSet->getLength())
+ return false;
+ if (!shouldCreateCalloc(Malloc, MemSet) ||
+ !DT.dominates(Malloc, MemSet) ||
+ !memoryIsNotModifiedBetween(Malloc, MemSet, BatchAA, DL, &DT))
+ return false;
+ } else {
+ // Handle zero store to small allocation.
+ assert(Store && "Expected Store");
+ ConstantInt *MallocSize = dyn_cast<ConstantInt>(Malloc->getOperand(0));
+ if (!MallocSize)
+ return false;
+ // Allow folding of stores of 1/2/4/8 bytes. The malloc size must match
+ // the store size.
+ uint64_t Size = MallocSize->getLimitedValue();
+ uint64_t StoreSize =
+ DL.getTypeStoreSize(Store->getValueOperand()->getType());
+ if (Size > 8 || (Size & (Size - 1)) || Size != StoreSize)
+ return false;
+ if (!shouldCreateCalloc(Malloc, Store) || !DT.dominates(Malloc, Store) ||
+ !memoryIsNotModifiedBetween(Malloc, Store, BatchAA, DL, &DT))
+ return false;
+ }
IRBuilder<> IRB(Malloc);
Type *SizeTTy = Malloc->getArgOperand(0)->getType();
auto *Calloc = emitCalloc(ConstantInt::get(SizeTTy, 1),
diff --git a/llvm/test/Transforms/DeadStoreElimination/noop-stores.ll b/llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
index 9fc20d76da5eb4..8b9a7b7ec128e5 100644
--- a/llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
@@ -350,6 +350,16 @@ define ptr @zero_memset_after_malloc_with_different_sizes(i64 %size) {
ret ptr %call
}
+define ptr @zero_store_after_malloc() {
+; CHECK-LABEL: @zero_store_after_malloc(
+; CHECK-NEXT: [[CALLOC:%.*]] = call ptr @calloc(i64 1, i64 8)
+; CHECK-NEXT: ret ptr [[CALLOC]]
+;
+ %call = call ptr @malloc(i64 8) inaccessiblememonly
+ store i64 0, ptr %call
+ ret ptr %call
+}
+
; based on pr25892_lite
define ptr @zero_memset_after_new(i64 %size) {
; CHECK-LABEL: @zero_memset_after_new(
diff --git a/llvm/test/Transforms/DeadStoreElimination/simple.ll b/llvm/test/Transforms/DeadStoreElimination/simple.ll
index ef2c4ef564b24a..6515657d89bff3 100644
--- a/llvm/test/Transforms/DeadStoreElimination/simple.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/simple.ll
@@ -204,10 +204,9 @@ define void @test_matrix_store(i64 %stride) {
declare void @may_unwind()
define ptr @test_malloc_no_escape_before_return() {
; CHECK-LABEL: @test_malloc_no_escape_before_return(
-; CHECK-NEXT: [[PTR:%.*]] = tail call ptr @malloc(i64 4)
+; CHECK-NEXT: [[CALLOC:%.*]] = call ptr @calloc(i64 1, i64 4)
; CHECK-NEXT: call void @may_unwind()
-; CHECK-NEXT: store i32 0, ptr [[PTR]], align 4
-; CHECK-NEXT: ret ptr [[PTR]]
+; CHECK-NEXT: ret ptr [[CALLOC]]
;
%ptr = tail call ptr @malloc(i64 4)
%DEAD = load i32, ptr %ptr
@@ -236,10 +235,9 @@ define ptr @test_custom_malloc_no_escape_before_return() {
define ptr addrspace(1) @test13_addrspacecast() {
; CHECK-LABEL: @test13_addrspacecast(
-; CHECK-NEXT: [[P:%.*]] = tail call ptr @malloc(i64 4)
-; CHECK-NEXT: [[P_AC:%.*]] = addrspacecast ptr [[P]] to ptr addrspace(1)
+; CHECK-NEXT: [[CALLOC:%.*]] = call ptr @calloc(i64 1, i64 4)
+; CHECK-NEXT: [[P_AC:%.*]] = addrspacecast ptr [[CALLOC]] to ptr addrspace(1)
; CHECK-NEXT: call void @may_unwind()
-; CHECK-NEXT: store i32 0, ptr addrspace(1) [[P_AC]], align 4
; CHECK-NEXT: ret ptr addrspace(1) [[P_AC]]
;
%p = tail call ptr @malloc(i64 4)
``````````
</details>
https://github.com/llvm/llvm-project/pull/106069
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