[llvm] r358303 - [MemorySSA] Small fix for the clobber limit.
Alina Sbirlea via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 12 11:48:46 PDT 2019
Author: asbirlea
Date: Fri Apr 12 11:48:46 2019
New Revision: 358303
URL: http://llvm.org/viewvc/llvm-project?rev=358303&view=rev
Log:
[MemorySSA] Small fix for the clobber limit.
Summary:
After introducing the limit for clobber walking, `walkToPhiOrClobber` would assert that the limit is at least 1 on entry.
The test included triggered that assert.
The callsite in `tryOptimizePhi` making the calls to `walkToPhiOrClobber` is structured like this:
```
while (true) {
if (getBlockingAccess()) { // calls walkToPhiOrClobber
}
for (...) {
walkToPhiOrClobber();
}
}
```
The cleanest fix is to check if the limit was reached inside `walkToPhiOrClobber`, and give an allowence of 1.
This approach not make any alias() calls (no calls to instructionClobbersQuery), so the performance condition is enforced.
The limit is set back to 0 if not used, as this provides info on the fact that we stopped before reaching a true clobber.
Reviewers: george.burgess.iv
Subscribers: jlebar, Prazek, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60479
Added:
llvm/trunk/test/Analysis/MemorySSA/reduce_clobber_limit.ll
Modified:
llvm/trunk/lib/Analysis/MemorySSA.cpp
Modified: llvm/trunk/lib/Analysis/MemorySSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemorySSA.cpp?rev=358303&r1=358302&r2=358303&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/MemorySSA.cpp (original)
+++ llvm/trunk/lib/Analysis/MemorySSA.cpp Fri Apr 12 11:48:46 2019
@@ -544,10 +544,15 @@ template <class AliasAnalysisType> class
const MemoryAccess *SkipStopAt = nullptr) const {
assert(!isa<MemoryUse>(Desc.Last) && "Uses don't exist in my world");
assert(UpwardWalkLimit && "Need a valid walk limit");
- // This will not do any alias() calls. It returns in the first iteration in
- // the loop below.
- if (*UpwardWalkLimit == 0)
- (*UpwardWalkLimit)++;
+ bool LimitAlreadyReached = false;
+ // (*UpwardWalkLimit) may be 0 here, due to the loop in tryOptimizePhi. Set
+ // it to 1. This will not do any alias() calls. It either returns in the
+ // first iteration in the loop below, or is set back to 0 if all def chains
+ // are free of MemoryDefs.
+ if (!*UpwardWalkLimit) {
+ *UpwardWalkLimit = 1;
+ LimitAlreadyReached = true;
+ }
for (MemoryAccess *Current : def_chain(Desc.Last)) {
Desc.Last = Current;
@@ -568,6 +573,9 @@ template <class AliasAnalysisType> class
}
}
+ if (LimitAlreadyReached)
+ *UpwardWalkLimit = 0;
+
assert(isa<MemoryPhi>(Desc.Last) &&
"Ended at a non-clobber that's not a phi?");
return {Desc.Last, false, MayAlias};
Added: llvm/trunk/test/Analysis/MemorySSA/reduce_clobber_limit.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/MemorySSA/reduce_clobber_limit.ll?rev=358303&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/MemorySSA/reduce_clobber_limit.ll (added)
+++ llvm/trunk/test/Analysis/MemorySSA/reduce_clobber_limit.ll Fri Apr 12 11:48:46 2019
@@ -0,0 +1,131 @@
+; RUN: opt -S -memoryssa %s | FileCheck %s
+; REQUIRES: asserts
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK-LABEL: @func()
+; Function Attrs: noinline
+define dso_local void @func() unnamed_addr #0 align 2 {
+entry:
+ %NoFinalize.addr = alloca i8, align 1
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ %call8 = call zeroext i1 @foo()
+ br i1 %call8, label %if.then9, label %while.cond
+
+if.then9: ; preds = %entry
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ br label %while.cond
+
+while.cond: ; preds = %cleanup, %if.then9, %entry
+ %call34 = call zeroext i1 @foo()
+ call void @blah()
+ br i1 %call34, label %while.body, label %while.end
+
+while.body: ; preds = %while.cond
+ %call35 = call zeroext i1 @foo()
+ br i1 %call35, label %if.end37, label %if.then36
+
+if.then36: ; preds = %while.body
+ store i32 2, i32* undef, align 4
+ br label %cleanup
+
+if.end37: ; preds = %while.body
+ %call38 = call zeroext i1 @foo()
+ br i1 %call38, label %if.end46, label %land.lhs.true
+
+land.lhs.true: ; preds = %if.end37
+ call void @blah()
+ %call41 = call zeroext i1 @foo()
+ br i1 %call41, label %if.then42, label %if.end46
+
+if.then42: ; preds = %land.lhs.true
+ call void @blah()
+ br label %if.end46
+
+if.end46: ; preds = %if.then42, %land.lhs.true, %if.end37
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ br label %cleanup
+
+cleanup: ; preds = %if.end46, %if.then36
+ call void @blah()
+ br label %while.cond
+
+while.end: ; preds = %while.cond
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ %call93 = call zeroext i1 @foo()
+ br i1 %call93, label %if.end120, label %if.then94
+
+if.then94: ; preds = %while.end
+ store i32 0, i32* undef, align 4
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ br label %for.cond
+
+for.cond: ; preds = %for.body, %if.then94
+ br i1 undef, label %for.body, label %if.end120
+
+for.body: ; preds = %for.cond
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ call void @blah()
+ br label %for.cond
+
+if.end120: ; preds = %for.cond, %while.end
+ %val = load i8, i8* %NoFinalize.addr, align 1
+ ret void
+}
+
+; Function Attrs: noinline
+declare hidden void @blah() unnamed_addr #0 align 2
+
+; Function Attrs: noinline
+declare hidden i1 @foo() local_unnamed_addr #0 align 2
+
+attributes #0 = { noinline }
+
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