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Teach InstCombine to eliminate malloc-realloc-free triplets. 

Reviewed By: majnemer

Differential Revision: https://reviews.llvm.org/D109988
This commit is contained in:
Owen Anderson 2021-09-17 18:28:58 +00:00
parent cbdf624bb8
commit b5fbbdd202
3 changed files with 59 additions and 0 deletions
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16
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -2596,6 +2596,13 @@ static bool isAllocSiteRemovable(Instruction *AI,
Users.emplace_back(I);
continue;
}
if (isReallocLikeFn(I, TLI, true)) {
Users.emplace_back(I);
Worklist.push_back(I);
continue;
}
return false;
case Instruction::Store: {
@ -2808,6 +2815,15 @@ Instruction *InstCombinerImpl::visitFree(CallInst &FI) {
if (isa<ConstantPointerNull>(Op))
return eraseInstFromFunction(FI);
// If we had free(realloc(...)) with no intervening uses, then eliminate the
// realloc() entirely.
if (CallInst *CI = dyn_cast<CallInst>(Op)) {
if (CI->hasOneUse() && isReallocLikeFn(CI, &TLI, true)) {
return eraseInstFromFunction(
*replaceInstUsesWith(*CI, CI->getOperand(0)));
}
}
// If we optimize for code size, try to move the call to free before the null
// test so that simplify cfg can remove the empty block and dead code
// elimination the branch. I.e., helps to turn something like:

24
llvm/test/Transforms/InstCombine/alloc-realloc-free.ll Normal file
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@ -0,0 +1,24 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --scrub-attributes
; RUN: opt -S -instcombine < %s | FileCheck %s
define dso_local void @test() local_unnamed_addr #0 {
; CHECK-LABEL: @test(
; CHECK-NEXT: ret void
;
%1 = tail call noalias align 16 dereferenceable_or_null(4) i8* @malloc(i64 4) #4
%2 = tail call align 16 dereferenceable_or_null(6) i8* @realloc(i8* %1, i64 6) #4
tail call void @free(i8* %2) #4
ret void
}
declare dso_local noalias noundef i8* @malloc(i64 noundef) local_unnamed_addr #1
declare dso_local noalias noundef i8* @realloc(i8* nocapture, i64 noundef) local_unnamed_addr #2
declare dso_local void @free(i8* nocapture noundef) local_unnamed_addr #2
declare void @llvm.dbg.value(metadata, metadata, metadata) #3
attributes #0 = { mustprogress nounwind uwtable willreturn }
attributes #1 = { inaccessiblememonly mustprogress nofree nounwind willreturn }
attributes #2 = { inaccessiblemem_or_argmemonly mustprogress nounwind willreturn }
attributes #3 = { nofree nosync nounwind readnone speculatable willreturn }
attributes #4 = { nounwind }

19
llvm/test/Transforms/InstCombine/realloc-free.ll Normal file
View File

@ -0,0 +1,19 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --scrub-attributes
; RUN: opt -S -instcombine < %s | FileCheck %s
define dso_local void @_Z3fooPv(i8* nocapture %0) local_unnamed_addr #0 {
; CHECK-LABEL: @_Z3fooPv(
; CHECK-NEXT: tail call void @free(i8* [[TMP0:%.*]])
; CHECK-NEXT: ret void
;
%2 = tail call align 16 dereferenceable_or_null(6) i8* @realloc(i8* %0, i64 6) #2
tail call void @free(i8* %2) #2
ret void
}
declare dso_local noalias noundef i8* @realloc(i8* nocapture, i64 noundef) local_unnamed_addr #1
declare dso_local void @free(i8* nocapture noundef) local_unnamed_addr #1
attributes #0 = { mustprogress nounwind uwtable willreturn }
attributes #1 = { inaccessiblemem_or_argmemonly mustprogress nounwind willreturn }
attributes #2 = { nounwind }