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InstCombine: Process addrspacecast uses in PointerReplacer (#91953)
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This was looking through an addrspacecast, and not finding a later
unfoldable cast to another address space. Fixes improperly deleting
a required alloca + memcpy and introducing an illegal addrspacecast.
    
This also required fixing some worklist management issues with
addrspacecast, and assuming that only memcpy sources could need
replacement.
    
Regresses one test function, but this looks like it optimized
before by accident. It never saw the pointer use by the call
to readonly_callee, which should require insertion of a new cast.
    
Fixes #68120
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@arsenm
arsenm committed May 15, 2024
1 parent 74d91d9 commit 847c83f
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Showing 3 changed files with 104 additions and 16 deletions.
33 changes: 18 additions & 15 deletions llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -342,9 +342,13 @@ bool PointerReplacer::collectUsersRecursive(Instruction &I) {
Worklist.insert(Inst);
} else if (isEqualOrValidAddrSpaceCast(Inst, FromAS)) {
Worklist.insert(Inst);
if (!collectUsersRecursive(*Inst))
return false;
} else if (Inst->isLifetimeStartOrEnd()) {
continue;
} else {
// TODO: For arbitrary uses with address space mismatches, should we check
// if we can introduce a valid addrspacecast?
LLVM_DEBUG(dbgs() << "Cannot handle pointer user: " << *U << '\n');
return false;
}
Expand Down Expand Up @@ -406,20 +410,18 @@ void PointerReplacer::replace(Instruction *I) {
NewSI->takeName(SI);
WorkMap[SI] = NewSI;
} else if (auto *MemCpy = dyn_cast<MemTransferInst>(I)) {
auto *SrcV = getReplacement(MemCpy->getRawSource());
// The pointer may appear in the destination of a copy, but we don't want to
// replace it.
if (!SrcV) {
assert(getReplacement(MemCpy->getRawDest()) &&
"destination not in replace list");
return;
}
auto *DestV = MemCpy->getRawDest();
auto *SrcV = MemCpy->getRawSource();

if (auto *DestReplace = getReplacement(DestV))
DestV = DestReplace;
if (auto *SrcReplace = getReplacement(SrcV))
SrcV = SrcReplace;

IC.Builder.SetInsertPoint(MemCpy);
auto *NewI = IC.Builder.CreateMemTransferInst(
MemCpy->getIntrinsicID(), MemCpy->getRawDest(), MemCpy->getDestAlign(),
SrcV, MemCpy->getSourceAlign(), MemCpy->getLength(),
MemCpy->isVolatile());
MemCpy->getIntrinsicID(), DestV, MemCpy->getDestAlign(), SrcV,
MemCpy->getSourceAlign(), MemCpy->getLength(), MemCpy->isVolatile());
AAMDNodes AAMD = MemCpy->getAAMetadata();
if (AAMD)
NewI->setAAMetadata(AAMD);
Expand All @@ -432,16 +434,17 @@ void PointerReplacer::replace(Instruction *I) {
assert(isEqualOrValidAddrSpaceCast(
ASC, V->getType()->getPointerAddressSpace()) &&
"Invalid address space cast!");
auto *NewV = V;

if (V->getType()->getPointerAddressSpace() !=
ASC->getType()->getPointerAddressSpace()) {
auto *NewI = new AddrSpaceCastInst(V, ASC->getType(), "");
NewI->takeName(ASC);
IC.InsertNewInstWith(NewI, ASC->getIterator());
NewV = NewI;
WorkMap[ASC] = NewI;
} else {
WorkMap[ASC] = V;
}
IC.replaceInstUsesWith(*ASC, NewV);
IC.eraseInstFromFunction(*ASC);

} else {
llvm_unreachable("should never reach here");
}
Expand Down
81 changes: 81 additions & 0 deletions llvm/test/Transforms/InstCombine/AMDGPU/issue68120.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,81 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -passes=instcombine %s | FileCheck %s

; It is illegal to pass ptr addrspace(4) in %arg by addrspacecasting
; to ptr addrspace(5) to pass off to the stack argument. A temporary
; alloca and memcpy is necessary.
define void @issue68120_invalid_addrspacecast_introduced_0(ptr addrspace(4) byref([56 x i8]) %arg) {
; CHECK-LABEL: define void @issue68120_invalid_addrspacecast_introduced_0(
; CHECK-SAME: ptr addrspace(4) byref([56 x i8]) [[ARG:%.*]]) {
; CHECK-NEXT: [[ADDRSPACECAST_0_TO_5:%.*]] = alloca [56 x i8], align 1, addrspace(5)
; CHECK-NEXT: call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) noundef align 1 dereferenceable(56) [[ADDRSPACECAST_0_TO_5]], ptr addrspace(4) noundef align 1 dereferenceable(56) [[ARG]], i64 56, i1 false)
; CHECK-NEXT: call void @byval_func(ptr addrspace(5) [[ADDRSPACECAST_0_TO_5]])
; CHECK-NEXT: ret void
;
%alloca = alloca [56 x i8], addrspace(5)
%alloca1 = alloca [56 x i8], addrspace(5)
call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) %alloca, ptr addrspace(4) %arg, i64 56, i1 false)
call void @llvm.memcpy.p5.p5.i64(ptr addrspace(5) %alloca1, ptr addrspace(5) %alloca, i64 56, i1 false)
%addrspacecast.alloca1 = addrspacecast ptr addrspace(5) %alloca1 to ptr
%addrspacecast.0.to.5 = addrspacecast ptr %addrspacecast.alloca1 to ptr addrspace(5)
call void @byval_func(ptr addrspace(5) %addrspacecast.0.to.5)
ret void
}

; Further reduced variant that already eliminated one of the copies
define void @issue68120_invalid_addrspacecast_introduced_1(ptr addrspace(4) byref([56 x i8]) %arg) {
; CHECK-LABEL: define void @issue68120_invalid_addrspacecast_introduced_1(
; CHECK-SAME: ptr addrspace(4) byref([56 x i8]) [[ARG:%.*]]) {
; CHECK-NEXT: [[ADDRSPACECAST_0_TO_5:%.*]] = alloca [56 x i8], align 1, addrspace(5)
; CHECK-NEXT: call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) noundef align 1 dereferenceable(56) [[ADDRSPACECAST_0_TO_5]], ptr addrspace(4) noundef align 1 dereferenceable(56) [[ARG]], i64 56, i1 false)
; CHECK-NEXT: call void @byval_func(ptr addrspace(5) [[ADDRSPACECAST_0_TO_5]])
; CHECK-NEXT: ret void
;
%alloca = alloca [56 x i8], addrspace(5)
call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) %alloca, ptr addrspace(4) %arg, i64 56, i1 false)
%addrspacecast.alloca = addrspacecast ptr addrspace(5) %alloca to ptr
%addrspacecast.0.to.5 = addrspacecast ptr %addrspacecast.alloca to ptr addrspace(5)
call void @byval_func(ptr addrspace(5) %addrspacecast.0.to.5)
ret void
}

define void @issue68120_use_cast_to_as0(ptr addrspace(4) byref([56 x i8]) %arg) {
; CHECK-LABEL: define void @issue68120_use_cast_to_as0(
; CHECK-SAME: ptr addrspace(4) byref([56 x i8]) [[ARG:%.*]]) {
; CHECK-NEXT: [[ALLOCA:%.*]] = alloca [56 x i8], align 1, addrspace(5)
; CHECK-NEXT: call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) noundef align 1 dereferenceable(56) [[ALLOCA]], ptr addrspace(4) noundef align 1 dereferenceable(56) [[ARG]], i64 56, i1 false)
; CHECK-NEXT: [[ADDRSPACECAST_ALLOCA:%.*]] = addrspacecast ptr addrspace(5) [[ALLOCA]] to ptr
; CHECK-NEXT: call void @other_func(ptr [[ADDRSPACECAST_ALLOCA]])
; CHECK-NEXT: ret void
;
%alloca = alloca [56 x i8], addrspace(5)
call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) %alloca, ptr addrspace(4) %arg, i64 56, i1 false)
%addrspacecast.alloca = addrspacecast ptr addrspace(5) %alloca to ptr
%addrspacecast.0.to.5 = addrspacecast ptr %addrspacecast.alloca to ptr addrspace(5)
call void @other_func(ptr %addrspacecast.alloca)
ret void
}

define void @issue68120_uses_invalid_addrspacecast(ptr addrspace(4) byref([56 x i8]) %arg) {
; CHECK-LABEL: define void @issue68120_uses_invalid_addrspacecast(
; CHECK-SAME: ptr addrspace(4) byref([56 x i8]) [[ARG:%.*]]) {
; CHECK-NEXT: [[ADDRSPACECAST_0_TO_5:%.*]] = alloca [56 x i8], align 1, addrspace(5)
; CHECK-NEXT: call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) noundef align 1 dereferenceable(56) [[ADDRSPACECAST_0_TO_5]], ptr addrspace(4) noundef align 1 dereferenceable(56) [[ARG]], i64 56, i1 false)
; CHECK-NEXT: call void @byval_func(ptr addrspace(5) [[ADDRSPACECAST_0_TO_5]])
; CHECK-NEXT: ret void
;
%alloca = alloca [56 x i8], addrspace(5)
%alloca1 = alloca [56 x i8], addrspace(5)
%illegal.cast = addrspacecast ptr addrspace(4) %arg to ptr addrspace(5)
call void @llvm.memcpy.p5.p5.i64(ptr addrspace(5) %alloca, ptr addrspace(5) %illegal.cast, i64 56, i1 false)
call void @llvm.memcpy.p5.p5.i64(ptr addrspace(5) %alloca1, ptr addrspace(5) %alloca, i64 56, i1 false)
%addrspacecast.alloca1 = addrspacecast ptr addrspace(5) %alloca1 to ptr
%addrspacecast.0.to.5 = addrspacecast ptr %addrspacecast.alloca1 to ptr addrspace(5)
call void @byval_func(ptr addrspace(5) %addrspacecast.0.to.5)
ret void
}


declare void @byval_func(ptr addrspace(5) byval([56 x i8]))
declare void @other_func(ptr)

6 changes: 5 additions & 1 deletion llvm/test/Transforms/InstCombine/ptr-replace-alloca.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -429,9 +429,13 @@ entry:

declare i8 @readonly_callee(ptr readonly nocapture)

; FIXME: This should be able to fold to call i8 @readonly_callee(ptr nonnull @g1)
define i8 @call_readonly_remove_alloca() {
; CHECK-LABEL: @call_readonly_remove_alloca(
; CHECK-NEXT: [[V:%.*]] = call i8 @readonly_callee(ptr nonnull @g1)
; CHECK-NEXT: [[ALLOCA:%.*]] = alloca [32 x i8], align 1, addrspace(1)
; CHECK-NEXT: call void @llvm.memcpy.p1.p0.i64(ptr addrspace(1) noundef align 1 dereferenceable(32) [[ALLOCA]], ptr noundef nonnull align 16 dereferenceable(32) @g1, i64 32, i1 false)
; CHECK-NEXT: [[P:%.*]] = addrspacecast ptr addrspace(1) [[ALLOCA]] to ptr
; CHECK-NEXT: [[V:%.*]] = call i8 @readonly_callee(ptr [[P]])
; CHECK-NEXT: ret i8 [[V]]
;
%alloca = alloca [32 x i8], addrspace(1)
Expand Down

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