[InstCombine] Don't replace allocas with smaller globals
Summary:
InstCombine replaces large allocas with small globals consts causing buffer overflows
on valid code, see PR33372.
This fix permits this optimization only if the global is dereference for alloca size.
Fixes PR33372
Reviewers: eugenis, majnemer, chandlerc
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D34311
llvm-svn: 306194
GitOrigin-RevId: df19ad456e7e21065a52bd9f3c0de6c7deb5195e
diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index a4d84ae..ee30aa4 100644
--- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -169,6 +169,18 @@
return nullptr;
}
+/// Returns true if V is dereferenceable for size of alloca.
+static bool isDereferenceableForAllocaSize(const Value *V, const AllocaInst *AI,
+ const DataLayout &DL) {
+ if (AI->isArrayAllocation())
+ return false;
+ uint64_t AllocaSize = DL.getTypeStoreSize(AI->getAllocatedType());
+ if (!AllocaSize)
+ return false;
+ return isDereferenceableAndAlignedPointer(V, AI->getAlignment(),
+ APInt(64, AllocaSize), DL);
+}
+
static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
// Check for array size of 1 (scalar allocation).
if (!AI.isArrayAllocation()) {
@@ -390,7 +402,8 @@
if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(&AI, ToDelete)) {
unsigned SourceAlign = getOrEnforceKnownAlignment(
Copy->getSource(), AI.getAlignment(), DL, &AI, &AC, &DT);
- if (AI.getAlignment() <= SourceAlign) {
+ if (AI.getAlignment() <= SourceAlign &&
+ isDereferenceableForAllocaSize(Copy->getSource(), &AI, DL)) {
DEBUG(dbgs() << "Found alloca equal to global: " << AI << '\n');
DEBUG(dbgs() << " memcpy = " << *Copy << '\n');
for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)
diff --git a/test/Transforms/InstCombine/memcpy-from-global.ll b/test/Transforms/InstCombine/memcpy-from-global.ll
index 7c9384d..c8b329e 100644
--- a/test/Transforms/InstCombine/memcpy-from-global.ll
+++ b/test/Transforms/InstCombine/memcpy-from-global.ll
@@ -204,3 +204,34 @@
; CHECK-NEXT: call void @bar(i8* bitcast (%U* getelementptr inbounds ([2 x %U], [2 x %U]* @H, i64 0, i64 1) to i8*))
ret void
}
+
+@bbb = local_unnamed_addr global [1000000 x i8] zeroinitializer, align 16
+@_ZL3KKK = internal unnamed_addr constant [3 x i8] c"\01\01\02", align 1
+
+; Should not replace alloca with global because of size mismatch.
+define void @test9_small_global() {
+; CHECK-LABEL: @test9_small_global(
+; CHECK-NOT: call void @llvm.memcpy.p0i8.p0i8.i64({{.*}}@bbb,{{.*}}@_ZL3KKK,
+; CHECK: alloca [1000000 x i8]
+entry:
+ %cc = alloca [1000000 x i8], align 16
+ %cc.0..sroa_idx = getelementptr inbounds [1000000 x i8], [1000000 x i8]* %cc, i64 0, i64 0
+ %arraydecay = getelementptr inbounds [1000000 x i8], [1000000 x i8]* %cc, i32 0, i32 0
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* %arraydecay, i8* getelementptr inbounds ([3 x i8], [3 x i8]* @_ZL3KKK, i32 0, i32 0), i64 3, i32 1, i1 false)
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* getelementptr inbounds ([1000000 x i8], [1000000 x i8]* @bbb, i32 0, i32 0), i8* %arraydecay, i64 1000000, i32 16, i1 false)
+ ret void
+}
+
+; Should replace alloca with global as they have exactly the same size.
+define void @test10_same_global() {
+; CHECK-LABEL: @test10_same_global(
+; CHECK-NOT: alloca
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64({{.*}}@bbb,{{.*}}@_ZL3KKK,{{.*}}, i64 3,
+entry:
+ %cc = alloca [3 x i8], align 1
+ %cc.0..sroa_idx = getelementptr inbounds [3 x i8], [3 x i8]* %cc, i64 0, i64 0
+ %arraydecay = getelementptr inbounds [3 x i8], [3 x i8]* %cc, i32 0, i32 0
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* %arraydecay, i8* getelementptr inbounds ([3 x i8], [3 x i8]* @_ZL3KKK, i32 0, i32 0), i64 3, i32 1, i1 false)
+ call void @llvm.memcpy.p0i8.p0i8.i64(i8* getelementptr inbounds ([1000000 x i8], [1000000 x i8]* @bbb, i32 0, i32 0), i8* %arraydecay, i64 3, i32 1, i1 false)
+ ret void
+}
