[llvm] r277978 - [MSSA] Fix PR28880 by fixing use optimizer's lower bound tracking behavior.
Daniel Berlin via llvm-commits
llvm-commits at lists.llvm.org
Sun Aug 7 21:44:53 PDT 2016
Author: dannyb
Date: Sun Aug 7 23:44:53 2016
New Revision: 277978
URL: http://llvm.org/viewvc/llvm-project?rev=277978&view=rev
Log:
[MSSA] Fix PR28880 by fixing use optimizer's lower bound tracking behavior.
Summary:
In the use optimizer, we need to keep of whether the lower bound still
dominates us or else we may decide a lower bound is still valid when it
is not due to intervening pushes/pops. Fixes PR28880 (and probably a
bunch of other things).
Reviewers: george.burgess.iv
Subscribers: MatzeB, llvm-commits, sebpop
Differential Revision: https://reviews.llvm.org/D23237
Added:
llvm/trunk/test/Transforms/Util/MemorySSA/pr28880.ll
Modified:
llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp
Modified: llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp?rev=277978&r1=277977&r2=277978&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/MemorySSA.cpp Sun Aug 7 23:44:53 2016
@@ -1288,6 +1288,7 @@ private:
// Note: Correctness depends on this being initialized to 0, which densemap
// does
unsigned long LowerBound;
+ const BasicBlock *LowerBoundBlock;
// This is where the last walk for this memory location ended.
unsigned long LastKill;
bool LastKillValid;
@@ -1333,7 +1334,6 @@ void MemorySSA::OptimizeUses::optimizeUs
VersionStack.pop_back();
++PopEpoch;
}
-
for (MemoryAccess &MA : *Accesses) {
auto *MU = dyn_cast<MemoryUse>(&MA);
if (!MU) {
@@ -1355,13 +1355,24 @@ void MemorySSA::OptimizeUses::optimizeUs
if (LocInfo.PopEpoch != PopEpoch) {
LocInfo.PopEpoch = PopEpoch;
LocInfo.StackEpoch = StackEpoch;
- // If the lower bound was in the info we popped, we have to reset it.
- if (LocInfo.LowerBound >= VersionStack.size()) {
+ // If the lower bound was in something that no longer dominates us, we
+ // have to reset it.
+ // We can't simply track stack size, because the stack may have had
+ // pushes/pops in the meantime.
+ // XXX: This is non-optimal, but only is slower cases with heavily
+ // branching dominator trees. To get the optimal number of queries would
+ // be to make lowerbound and lastkill a per-loc stack, and pop it until
+ // the top of that stack dominates us. This does not seem worth it ATM.
+ // A much cheaper optimization would be to always explore the deepest
+ // branch of the dominator tree first. This will guarantee this resets on
+ // the smallest set of blocks.
+ if (LocInfo.LowerBoundBlock && LocInfo.LowerBoundBlock != BB &&
+ !DT->dominates(LocInfo.LowerBoundBlock, BB)){
// Reset the lower bound of things to check.
// TODO: Some day we should be able to reset to last kill, rather than
// 0.
-
LocInfo.LowerBound = 0;
+ LocInfo.LowerBoundBlock = VersionStack[0]->getBlock();
LocInfo.LastKillValid = false;
}
} else if (LocInfo.StackEpoch != StackEpoch) {
@@ -1437,6 +1448,7 @@ void MemorySSA::OptimizeUses::optimizeUs
MU->setDefiningAccess(VersionStack[LocInfo.LastKill]);
}
LocInfo.LowerBound = VersionStack.size() - 1;
+ LocInfo.LowerBoundBlock = BB;
}
}
Added: llvm/trunk/test/Transforms/Util/MemorySSA/pr28880.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Util/MemorySSA/pr28880.ll?rev=277978&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/Util/MemorySSA/pr28880.ll (added)
+++ llvm/trunk/test/Transforms/Util/MemorySSA/pr28880.ll Sun Aug 7 23:44:53 2016
@@ -0,0 +1,51 @@
+; RUN: opt -basicaa -print-memoryssa -verify-memoryssa -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 testcase is reduced from SingleSource/Benchmarks/Misc/fbench.c
+; It is testing to make sure that the MemorySSA use optimizer
+; comes up with right answers when dealing with multiple MemoryLocations
+; over different blocks. See PR28880 for more details.
+ at global = external hidden unnamed_addr global double, align 8
+ at global.1 = external hidden unnamed_addr global double, align 8
+
+; Function Attrs: nounwind ssp uwtable
+define hidden fastcc void @hoge() unnamed_addr #0 {
+bb:
+ br i1 undef, label %bb1, label %bb2
+
+bb1: ; preds = %bb
+; These accesses should not conflict.
+; CHECK: 1 = MemoryDef(liveOnEntry)
+; 1 = MemoryDef(liveOnEntry)
+; CHECK-NEXT: store double undef, double* @global, align 8
+ store double undef, double* @global, align 8
+; CHECK: MemoryUse(liveOnEntry)
+; MemoryUse(liveOnEntry)
+; CHECK-NEXT: %tmp = load double, double* @global.1, align 8
+ %tmp = load double, double* @global.1, align 8
+ unreachable
+
+bb2: ; preds = %bb
+ br label %bb3
+
+bb3: ; preds = %bb2
+ br i1 undef, label %bb4, label %bb6
+
+bb4: ; preds = %bb3
+; These accesses should conflict.
+; CHECK: 2 = MemoryDef(liveOnEntry)
+; 2 = MemoryDef(liveOnEntry)
+; CHECK-NEXT: store double 0.000000e+00, double* @global.1, align 8
+ store double 0.000000e+00, double* @global.1, align 8
+; CHECK: MemoryUse(2)
+; MemoryUse(2)
+; CHECK-NEXT: %tmp5 = load double, double* @global.1, align 8
+ %tmp5 = load double, double* @global.1, align 8
+ unreachable
+
+bb6: ; preds = %bb3
+ unreachable
+}
+
+attributes #0 = { nounwind ssp uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="core2" "target-features"="+cx16,+fxsr,+mmx,+sse,+sse2,+sse3,+ssse3" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
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