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[InstCombine] tmp alloca bypass: ensure that the replacement dominates all alloca uses

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After 077bff39d46364035a5dcfa32fc69910ad0975d0,
isDereferenceableForAllocaSize() can recurse into selects,
which is causing a problem for the new test case,
reduced from https://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20210412/904154.html
because the replacement (the select) is defined after the first use
of an alloca, so we'd end up with a verifier error.

Now, this new check is too restrictive.
We likely can handle *some* cases, by trying to sink all uses of an alloca
to after the the def.
This commit is contained in:
Roman Lebedev 2021-04-14 13:02:20 +03:00
parent 199c80bef9
commit f71031c386
3 changed files with 45 additions and 4 deletions
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6
lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
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@ -406,7 +406,11 @@ Instruction *InstCombinerImpl::visitAllocaInst(AllocaInst &AI) {
Align SourceAlign = getOrEnforceKnownAlignment(
TheSrc, AllocaAlign, DL, &AI, &AC, &DT);
if (AllocaAlign <= SourceAlign &&
isDereferenceableForAllocaSize(TheSrc, &AI, DL)) {
isDereferenceableForAllocaSize(TheSrc, &AI, DL) &&
(!isa<Instruction>(TheSrc) || all_of(AI.users(), [&](const User *U) {
return DT.dominates(cast<Instruction>(TheSrc), cast<Instruction>(U));
}))) {
// FIXME: can the dominance restriction be relaxed by sinking instrns?
LLVM_DEBUG(dbgs() << "Found alloca equal to global: " << AI << '\n');
LLVM_DEBUG(dbgs() << " memcpy = " << *Copy << '\n');
unsigned SrcAddrSpace = TheSrc->getType()->getPointerAddressSpace();

8
test/Transforms/InstCombine/AMDGPU/memcpy-from-constant.ll
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@ -135,10 +135,12 @@ define amdgpu_kernel void @memcpy_constant_byref_arg_ptr_to_alloca_too_many_byte
; Simple memcpy to alloca from constant address space intrinsic call
define amdgpu_kernel void @memcpy_constant_intrinsic_ptr_to_alloca(i8 addrspace(1)* %out, i32 %idx) {
; CHECK-LABEL: @memcpy_constant_intrinsic_ptr_to_alloca(
; CHECK-NEXT: [[ALLOCA:%.*]] = alloca [32 x i8], align 4, addrspace(5)
; CHECK-NEXT: [[ALLOCA_CAST:%.*]] = getelementptr inbounds [32 x i8], [32 x i8] addrspace(5)* [[ALLOCA]], i32 0, i32 0
; CHECK-NEXT: [[KERNARG_SEGMENT_PTR:%.*]] = call align 16 dereferenceable(32) i8 addrspace(4)* @llvm.amdgcn.kernarg.segment.ptr()
; CHECK-NEXT: [[TMP1:%.*]] = sext i32 [[IDX:%.*]] to i64
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i8, i8 addrspace(4)* [[KERNARG_SEGMENT_PTR]], i64 [[TMP1]]
; CHECK-NEXT: [[LOAD:%.*]] = load i8, i8 addrspace(4)* [[GEP]], align 1
; CHECK-NEXT: call void @llvm.memcpy.p5i8.p4i8.i64(i8 addrspace(5)* noundef align 4 dereferenceable(32) [[ALLOCA_CAST]], i8 addrspace(4)* noundef align 16 dereferenceable(32) [[KERNARG_SEGMENT_PTR]], i64 32, i1 false)
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds [32 x i8], [32 x i8] addrspace(5)* [[ALLOCA]], i32 0, i32 [[IDX:%.*]]
; CHECK-NEXT: [[LOAD:%.*]] = load i8, i8 addrspace(5)* [[GEP]], align 1
; CHECK-NEXT: store i8 [[LOAD]], i8 addrspace(1)* [[OUT:%.*]], align 1
; CHECK-NEXT: ret void
;

35
test/Transforms/InstCombine/tmp-alloca-bypass.ll Normal file
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@ -0,0 +1,35 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -instcombine -S | FileCheck %s
; See https://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20210412/904154.html
; When replacing an allocation that is only modified by a memcpy/memmove from
; a constant whose alignment is equal to or exceeds that of the allocation,
; we also need to ensure that we actually can replace all uses of an alloca
; with said constant. This matters because it could be e.g. a select between
; two constants, that happens after the first use of an alloca.
%t0 = type { i8*, i64 }
@g0 = external constant %t0
@g1 = external constant %t0
define void @test(i8*%out) {
; CHECK-LABEL: @test(
; CHECK-NEXT: [[I0:%.*]] = alloca [[T0:%.*]], align 8
; CHECK-NEXT: [[I1:%.*]] = bitcast %t0* [[I0]] to i8*
; CHECK-NEXT: [[I2:%.*]] = call i1 @get_cond()
; CHECK-NEXT: [[I3:%.*]] = select i1 [[I2]], i8* bitcast (%t0* @g0 to i8*), i8* bitcast (%t0* @g1 to i8*)
; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* noundef nonnull align 8 dereferenceable(16) [[I1]], i8* noundef nonnull align 8 dereferenceable(16) [[I3]], i64 16, i1 false)
; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* noundef nonnull align 1 dereferenceable(16) [[OUT:%.*]], i8* noundef nonnull align 8 dereferenceable(16) [[I1]], i64 16, i1 false)
; CHECK-NEXT: ret void
;
%i0 = alloca %t0
%i1 = bitcast %t0* %i0 to i8*
%i2 = call i1 @get_cond()
%i3 = select i1 %i2, i8* bitcast (%t0* @g0 to i8*), i8* bitcast (%t0* @g1 to i8*)
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %i1, i8* %i3, i64 16, i1 false)
call void @llvm.memcpy.p0i8.p0i8.i64(i8* %out, i8* %i1, i64 16, i1 false)
ret void
}
declare i1 @get_cond()
declare void @llvm.memcpy.p0i8.p0i8.i64(i8*, i8*, i64, i1)