[llvm] be9889b - [MemorySSA] Don't treat lifetime.end as NoAlias
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Thu Feb 4 12:10:29 PST 2021
Author: Nikita Popov
Date: 2021-02-04T20:58:28+01:00
New Revision: be9889b350f47319b795a4a4826b4b0bc190807a
URL: https://github.com/llvm/llvm-project/commit/be9889b350f47319b795a4a4826b4b0bc190807a
DIFF: https://github.com/llvm/llvm-project/commit/be9889b350f47319b795a4a4826b4b0bc190807a.diff
LOG: [MemorySSA] Don't treat lifetime.end as NoAlias
MemorySSA currently treats lifetime.end intrinsics as not aliasing
anything. This breaks MemorySSA-based MemCpyOpt, because we'll happily
move a read of a pointer below a lifetime.end intrinsic, as no clobber
is reported.
I think the MemorySSA modelling here isn't correct: lifetime.end(p)
has approximately the same effect as doing a memcpy(p, undef), and
should be treated as a clobber.
This patch removes the special handling of lifetime.end, leaving
alias analysis to handle it appropriately.
Differential Revision: https://reviews.llvm.org/D95763
Added:
Modified:
llvm/lib/Analysis/MemorySSA.cpp
llvm/test/Analysis/MemorySSA/lifetime-simple.ll
llvm/test/Transforms/MemCpyOpt/lifetime.ll
Removed:
################################################################################
diff --git a/llvm/lib/Analysis/MemorySSA.cpp b/llvm/lib/Analysis/MemorySSA.cpp
index 57f1dcca0679..de9a28a8d004 100644
--- a/llvm/lib/Analysis/MemorySSA.cpp
+++ b/llvm/lib/Analysis/MemorySSA.cpp
@@ -282,7 +282,6 @@ instructionClobbersQuery(const MemoryDef *MD, const MemoryLocation &UseLoc,
// clobbers where they don't really exist at all. Please see D43269 for
// context.
switch (II->getIntrinsicID()) {
- case Intrinsic::lifetime_end:
case Intrinsic::invariant_start:
case Intrinsic::invariant_end:
case Intrinsic::assume:
@@ -359,22 +358,6 @@ struct UpwardsMemoryQuery {
} // end anonymous namespace
-static bool lifetimeEndsAt(MemoryDef *MD, const MemoryLocation &Loc,
- BatchAAResults &AA) {
- Instruction *Inst = MD->getMemoryInst();
- if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
- switch (II->getIntrinsicID()) {
- case Intrinsic::lifetime_end: {
- MemoryLocation ArgLoc = MemoryLocation::getAfter(II->getArgOperand(1));
- return AA.alias(ArgLoc, Loc) == MustAlias;
- }
- default:
- return false;
- }
- }
- return false;
-}
-
template <typename AliasAnalysisType>
static bool isUseTriviallyOptimizableToLiveOnEntry(AliasAnalysisType &AA,
const Instruction *I) {
@@ -1466,15 +1449,6 @@ void MemorySSA::OptimizeUses::optimizeUsesInBlock(
}
MemoryDef *MD = cast<MemoryDef>(VersionStack[UpperBound]);
- // If the lifetime of the pointer ends at this instruction, it's live on
- // entry.
- if (!UseMLOC.IsCall && lifetimeEndsAt(MD, UseMLOC.getLoc(), *AA)) {
- // Reset UpperBound to liveOnEntryDef's place in the stack
- UpperBound = 0;
- FoundClobberResult = true;
- LocInfo.AR = MustAlias;
- break;
- }
ClobberAlias CA = instructionClobbersQuery(MD, MU, UseMLOC, *AA);
if (CA.IsClobber) {
FoundClobberResult = true;
diff --git a/llvm/test/Analysis/MemorySSA/lifetime-simple.ll b/llvm/test/Analysis/MemorySSA/lifetime-simple.ll
index 33327c5539f6..2d0481c18415 100644
--- a/llvm/test/Analysis/MemorySSA/lifetime-simple.ll
+++ b/llvm/test/Analysis/MemorySSA/lifetime-simple.ll
@@ -1,8 +1,7 @@
; RUN: opt -basic-aa -print-memoryssa -verify-memoryssa -enable-new-pm=0 -analyze < %s 2>&1 | FileCheck %s
; RUN: opt -aa-pipeline=basic-aa -passes='print<memoryssa>,verify<memoryssa>' -disable-output < %s 2>&1 | FileCheck %s
-; This test checks a number of things:
-; First, the lifetime markers should not clobber any uses of Q or P.
-; Second, the loads of P are MemoryUse(LiveOnEntry) due to the placement of the markers vs the loads.
+; This test checks that lifetime markers are considered clobbers of %P,
+; and due to lack of noalias information, of %Q as well.
define i8 @test(i8* %P, i8* %Q) {
entry:
@@ -18,10 +17,10 @@ entry:
; CHECK: 3 = MemoryDef(2)
; CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 32, i8* %P)
call void @llvm.lifetime.end.p0i8(i64 32, i8* %P)
-; CHECK: MemoryUse(liveOnEntry)
+; CHECK: MemoryUse(3)
; CHECK-NEXT: %1 = load i8, i8* %P
%1 = load i8, i8* %P
-; CHECK: MemoryUse(2)
+; CHECK: MemoryUse(3)
; CHECK-NEXT: %2 = load i8, i8* %Q
%2 = load i8, i8* %Q
ret i8 %1
diff --git a/llvm/test/Transforms/MemCpyOpt/lifetime.ll b/llvm/test/Transforms/MemCpyOpt/lifetime.ll
index 5dc13ca10054..c7e7666307ab 100644
--- a/llvm/test/Transforms/MemCpyOpt/lifetime.ll
+++ b/llvm/test/Transforms/MemCpyOpt/lifetime.ll
@@ -1,6 +1,6 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -O2 -S -enable-memcpyopt-memoryssa=0 | FileCheck %s --check-prefixes=CHECK,NO_MSSA
-; RUN: opt < %s -O2 -S -enable-memcpyopt-memoryssa=1 -verify-memoryssa | FileCheck %s --check-prefixes=CHECK,MSSA
+; RUN: opt < %s -O2 -S -enable-memcpyopt-memoryssa=0 | FileCheck %s
+; RUN: opt < %s -O2 -S -enable-memcpyopt-memoryssa=1 -verify-memoryssa | FileCheck %s
; performCallSlotOptzn in MemCpy should not exchange the calls to
; @llvm.lifetime.start and @llvm.memcpy.
@@ -27,29 +27,17 @@ bb:
ret void
}
-; FIXME: Miscompile.
define void @memcpy_memcpy_across_lifetime(i8* noalias %p1, i8* noalias %p2, i8* noalias %p3) {
-; NO_MSSA-LABEL: @memcpy_memcpy_across_lifetime(
-; NO_MSSA-NEXT: [[A:%.*]] = alloca [16 x i8], align 1
-; NO_MSSA-NEXT: [[A8:%.*]] = getelementptr inbounds [16 x i8], [16 x i8]* [[A]], i64 0, i64 0
-; NO_MSSA-NEXT: call void @llvm.lifetime.start.p0i8(i64 16, i8* nonnull [[A8]])
-; NO_MSSA-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[A8]], i8* nonnull align 1 dereferenceable(16) [[P1:%.*]], i64 16, i1 false)
-; NO_MSSA-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[P1]], i8* nonnull align 1 dereferenceable(16) [[P2:%.*]], i64 16, i1 false)
-; NO_MSSA-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[P2]], i8* nonnull align 1 dereferenceable(16) [[A8]], i64 16, i1 false)
-; NO_MSSA-NEXT: call void @llvm.lifetime.end.p0i8(i64 16, i8* nonnull [[A8]])
-; NO_MSSA-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[P3:%.*]], i8* nonnull align 1 dereferenceable(16) [[P2]], i64 16, i1 false)
-; NO_MSSA-NEXT: ret void
-;
-; MSSA-LABEL: @memcpy_memcpy_across_lifetime(
-; MSSA-NEXT: [[A:%.*]] = alloca [16 x i8], align 1
-; MSSA-NEXT: [[A8:%.*]] = getelementptr inbounds [16 x i8], [16 x i8]* [[A]], i64 0, i64 0
-; MSSA-NEXT: call void @llvm.lifetime.start.p0i8(i64 16, i8* nonnull [[A8]])
-; MSSA-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[A8]], i8* nonnull align 1 dereferenceable(16) [[P1:%.*]], i64 16, i1 false)
-; MSSA-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[P1]], i8* nonnull align 1 dereferenceable(16) [[P2:%.*]], i64 16, i1 false)
-; MSSA-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[P2]], i8* nonnull align 1 dereferenceable(16) [[A8]], i64 16, i1 false)
-; MSSA-NEXT: call void @llvm.lifetime.end.p0i8(i64 16, i8* nonnull [[A8]])
-; MSSA-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[P3:%.*]], i8* nonnull align 1 dereferenceable(16) [[A8]], i64 16, i1 false)
-; MSSA-NEXT: ret void
+; CHECK-LABEL: @memcpy_memcpy_across_lifetime(
+; CHECK-NEXT: [[A:%.*]] = alloca [16 x i8], align 1
+; CHECK-NEXT: [[A8:%.*]] = getelementptr inbounds [16 x i8], [16 x i8]* [[A]], i64 0, i64 0
+; CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 16, i8* nonnull [[A8]])
+; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[A8]], i8* nonnull align 1 dereferenceable(16) [[P1:%.*]], i64 16, i1 false)
+; CHECK-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[P1]], i8* nonnull align 1 dereferenceable(16) [[P2:%.*]], i64 16, i1 false)
+; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[P2]], i8* nonnull align 1 dereferenceable(16) [[A8]], i64 16, i1 false)
+; CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 16, i8* nonnull [[A8]])
+; CHECK-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(16) [[P3:%.*]], i8* nonnull align 1 dereferenceable(16) [[P2]], i64 16, i1 false)
+; CHECK-NEXT: ret void
;
%a = alloca [16 x i8]
%a8 = bitcast [16 x i8]* %a to i8*
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