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[CodeGenPrepare] avoid crashing from replacing a phi twice

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Summary:
This is a fix to bug 41052:
https://bugs.llvm.org/show_bug.cgi?id=41052

While trying to optimize a memory instruction in a dead basic block, we end up registering the same phi for replacement twice. This patch avoids registering more than the first replacement candidate for a phi.

Patch by: JesperAntonsson

Reviewers: skatkov, aprantl

Reviewed By: aprantl

Subscribers: jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59358

llvm-svn: 356260
This commit is contained in:
Mikael Holmen 2019-03-15 13:51:05 +00:00
parent 26b46594cf
commit 9f277da942
2 changed files with 51 additions and 2 deletions
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8
lib/CodeGen/CodeGenPrepare.cpp
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@ -3282,6 +3282,8 @@ private:
PhiNodeSet &PhiNodesToMatch) {
SmallVector<PHIPair, 8> WorkList;
Matcher.insert({ PHI, Candidate });
SmallSet<PHINode *, 8> MatchedPHIs;
MatchedPHIs.insert(PHI);
WorkList.push_back({ PHI, Candidate });
SmallSet<PHIPair, 8> Visited;
while (!WorkList.empty()) {
@ -3314,8 +3316,10 @@ private:
if (Matcher.count({ FirstPhi, SecondPhi }))
continue;
// So the values are different and does not match. So we need them to
// match.
Matcher.insert({ FirstPhi, SecondPhi });
// match. (But we register no more than one match per PHI node, so that
// we won't later try to replace them twice.)
if (!MatchedPHIs.insert(FirstPhi).second)
Matcher.insert({ FirstPhi, SecondPhi });
// But me must check it.
WorkList.push_back({ FirstPhi, SecondPhi });
}

45
test/CodeGen/X86/codegen-prepare-replacephi.mir Normal file
View File

@ -0,0 +1,45 @@
# RUN: llc -run-pass=codegenprepare -o - %s | FileCheck %s
# This testcase without the accompanying fix triggers the assert
# "Replacement PHI node is already replaced."
--- |
define void @f1() {
entry:
%arrayidx = getelementptr inbounds [2 x i16], [2 x i16]* undef, i16 0, i16 2
%0 = bitcast i16* %arrayidx to i32*
%1 = bitcast [2 x i16]* undef to i32*
br label %for.cond
for.cond:
%2 = phi i32* [ %0, %entry ], [ %7, %cleanup ]
%3 = phi i32* [ %0, %entry ], [ %9, %cleanup ]
br label %for.body
for.body:
%4 = phi i32* [ %3, %for.cond ], [ %9, %cleanup ]
%5 = phi i32* [ %2, %for.cond ], [ %9, %cleanup ]
%6 = phi i32* [ %2, %for.cond ], [ %9, %cleanup ]
br i1 false, label %for.cond2, label %if.then
if.then:
store i32 undef, i32* %4, align 1
unreachable
for.cond2:
%7 = phi i32* [ %6, %for.body ], [ %7, %if.then5 ], [ %1, %for.cond2 ]
%8 = phi i32* [ %5, %for.body ], [ %8, %if.then5 ], [ %1, %for.cond2 ]
%9 = phi i32* [ %4, %for.body ], [ %8, %if.then5 ], [ %1, %for.cond2 ]
br i1 undef, label %for.cond2, label %if.then5
if.then5:
br i1 undef, label %cleanup, label %for.cond2
cleanup:
br i1 true, label %for.cond, label %for.body
}
...
# Sanity check to verify that something got through.
# CHECK-LABEL: entry: