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[CodeExtractor] Fix sinking of allocas with multiple bitcast uses (PR…
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…42451)

An alloca which can be sunk into the extraction region may have more
than one bitcast use. Move these uses along with the alloca to prevent
use-before-def.

Testing: check-llvm, stage2 build of clang

Fixes llvm.org/PR42451.

Differential Revision: https://reviews.llvm.org/D64463

llvm-svn: 365660
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@vedantk
vedantk committed Jul 10, 2019
1 parent f65f302 commit 5eb6ba0
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Showing 3 changed files with 104 additions and 14 deletions.
42 changes: 29 additions & 13 deletions llvm/lib/Transforms/Utils/CodeExtractor.cpp
View file
Expand Up @@ -519,18 +519,20 @@ void CodeExtractor::findAllocas(ValueSet &SinkCands, ValueSet &HoistCands,
if (Bitcasts.empty())
continue;

Instruction *BitcastAddr = Bitcasts.back();
const LifetimeMarkerInfo &LMI = BitcastLifetimeInfo.back();
assert(LMI.LifeStart &&
"Unsafe to sink bitcast without lifetime markers");
moveOrIgnoreLifetimeMarkers(LMI);
if (!definedInRegion(Blocks, BitcastAddr)) {
LLVM_DEBUG(dbgs() << "Sinking bitcast-of-alloca: " << *BitcastAddr
<< "\n");
SinkCands.insert(BitcastAddr);
}
LLVM_DEBUG(dbgs() << "Sinking alloca (via bitcast): " << *AI << "\n");
SinkCands.insert(AI);
for (unsigned I = 0, E = Bitcasts.size(); I != E; ++I) {
Instruction *BitcastAddr = Bitcasts[I];
const LifetimeMarkerInfo &LMI = BitcastLifetimeInfo[I];
assert(LMI.LifeStart &&
"Unsafe to sink bitcast without lifetime markers");
moveOrIgnoreLifetimeMarkers(LMI);
if (!definedInRegion(Blocks, BitcastAddr)) {
LLVM_DEBUG(dbgs() << "Sinking bitcast-of-alloca: " << *BitcastAddr
<< "\n");
SinkCands.insert(BitcastAddr);
}
}
}
}
}
Expand Down Expand Up @@ -1431,9 +1433,23 @@ Function *CodeExtractor::extractCodeRegion() {
findInputsOutputs(inputs, outputs, SinkingCands);

// Now sink all instructions which only have non-phi uses inside the region.
for (auto *II : SinkingCands)
cast<Instruction>(II)->moveBefore(*newFuncRoot,
newFuncRoot->getFirstInsertionPt());
// Group the allocas at the start of the block, so that any bitcast uses of
// the allocas are well-defined.
AllocaInst *FirstSunkAlloca = nullptr;
for (auto *II : SinkingCands) {
if (auto *AI = dyn_cast<AllocaInst>(II)) {
AI->moveBefore(*newFuncRoot, newFuncRoot->getFirstInsertionPt());
if (!FirstSunkAlloca)
FirstSunkAlloca = AI;
}
}
assert((SinkingCands.empty() || FirstSunkAlloca) &&
"Did not expect a sink candidate without any allocas");
for (auto *II : SinkingCands) {
if (!isa<AllocaInst>(II)) {
cast<Instruction>(II)->moveAfter(FirstSunkAlloca);
}
}

if (!HoistingCands.empty()) {
auto *HoistToBlock = findOrCreateBlockForHoisting(CommonExit);
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/CodeExtractor/live_shrink_multiple.ll
View file
Expand Up @@ -45,9 +45,9 @@ bb:
; CHECK-LABEL: define internal void @_Z3foov.1.
; CHECK: newFuncRoot:
; CHECK-NEXT: alloca
; CHECK-NEXT: alloca
; CHECK-NEXT: bitcast
; CHECK-NEXT: call void @llvm.lifetime.start.p0i8
; CHECK-NEXT: alloca
; CHECK-NEXT: bitcast
; CHECK-NEXT: call void @llvm.lifetime.start.p0i8
; CHECK: call void @llvm.lifetime.end.p0i8
Expand Down
74 changes: 74 additions & 0 deletions llvm/test/Transforms/HotColdSplit/sink-multiple-bitcasts-of-allocas-pr42451.ll
View file
@@ -0,0 +1,74 @@
; RUN: opt -hotcoldsplit -hotcoldsplit-threshold=-1 -S < %s | FileCheck %s

target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.14.0"

@c = common global i32 0, align 4
@h = common global i32 0, align 4

declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1

declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1

declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg) #1

declare i32* @m()

; CHECK-LABEL: define void @main()
; CHECK-NEXT: %.sroa.4.i = alloca [20 x i8], align 2
; CHECK-NEXT: %.sroa.5.i = alloca [6 x i8], align 8
; CHECK-NEXT: %1 = bitcast [6 x i8]* %.sroa.5.i to i8*

define void @main() #0 {
%.sroa.4.i = alloca [20 x i8], align 2
%.sroa.5.i = alloca [6 x i8], align 8
%1 = bitcast [6 x i8]* %.sroa.5.i to i8*
%2 = load i32, i32* @h, align 4, !tbaa !4
%3 = icmp ne i32 %2, 0
br i1 %3, label %12, label %4

4: ; preds = %0
%5 = call i32* @m() #3
%.sroa.4.0..sroa_idx21.i = getelementptr inbounds [20 x i8], [20 x i8]* %.sroa.4.i, i64 0, i64 0
call void @llvm.lifetime.start.p0i8(i64 20, i8* %.sroa.4.0..sroa_idx21.i) #3
%.sroa.5.0..sroa_idx16.i = getelementptr inbounds [6 x i8], [6 x i8]* %.sroa.5.i, i64 0, i64 0
call void @llvm.lifetime.start.p0i8(i64 6, i8* %.sroa.5.0..sroa_idx16.i) #3
call void @llvm.memset.p0i8.i64(i8* align 2 %.sroa.4.0..sroa_idx21.i, i8 0, i64 20, i1 false) #3
call void @llvm.memset.p0i8.i64(i8* align 8 %.sroa.5.0..sroa_idx16.i, i8 0, i64 6, i1 false) #3
%6 = load i32, i32* @c, align 4, !tbaa !4
%7 = trunc i32 %6 to i16
call void @llvm.lifetime.end.p0i8(i64 20, i8* %.sroa.4.0..sroa_idx21.i) #3
call void @llvm.lifetime.end.p0i8(i64 6, i8* %.sroa.5.0..sroa_idx16.i) #3
call void @llvm.lifetime.start.p0i8(i64 6, i8* %1) #3
call void @llvm.memset.p0i8.i64(i8* align 1 %1, i8 3, i64 6, i1 false)
br label %8

8: ; preds = %8, %4
%.0.i = phi i32 [ 0, %4 ], [ %10, %8 ]
%9 = sext i32 %.0.i to i64
%10 = add nsw i32 %.0.i, 1
%11 = icmp slt i32 %10, 6
br i1 %11, label %8, label %l.exit

l.exit: ; preds = %8
call void @llvm.lifetime.end.p0i8(i64 6, i8* %1) #3
br label %12

12: ; preds = %l.exit, %0
%13 = phi i1 [ true, %0 ], [ true, %l.exit ]
ret void
}

attributes #0 = { cold }

!llvm.module.flags = !{!0, !1, !2}
!llvm.ident = !{!3}

!0 = !{i32 2, !"SDK Version", [2 x i32] [i32 10, i32 14]}
!1 = !{i32 1, !"wchar_size", i32 4}
!2 = !{i32 7, !"PIC Level", i32 2}
!3 = !{!"Apple clang version 11.0.0 (clang-1100.0.20.17)"}
!4 = !{!5, !5, i64 0}
!5 = !{!"int", !6, i64 0}
!6 = !{!"omnipotent char", !7, i64 0}
!7 = !{!"Simple C/C++ TBAA"}

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