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[MergeICmps] Do not perform the transformation if GEP is used outside of block

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Summary:
This patch prevents MergeICmps to performn the transformation if the address operand GEP of the load instruction has a use outside of the load's parent block. Without this patch, compiler crashes with the given test case because the use of `%first.i` is still around when the basic block is erased from https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/Scalar/MergeICmps.cpp#L620. I think checking `isUsedOutsideOfBlock` with `GEP` is the original intention of the code, as the checking for `LoadI` is already performed in the same function.

This patch is incomplete though, as this makes the pass overly conservative and fails the test `tuple-four-int8.ll`. I believe what needs to be done is checking if GEP has a use outside of block that is not the part of "Comparisons" chain. Submit the patch as of now to prevent compiler crash.

Reviewers: courbet, trentxintong

Reviewed By: courbet

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D54089

llvm-svn: 346151
This commit is contained in:
Taewook Oh 2018-11-05 18:16:32 +00:00
parent f2eec24b6f
commit 956f97e693
3 changed files with 38 additions and 1 deletions
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2
lib/Transforms/Scalar/MergeICmps.cpp
View File

@ -98,7 +98,7 @@ BCEAtom visitICmpLoadOperand(Value *const Val) {
Value *const Addr = LoadI->getOperand(0);
if (auto *const GEP = dyn_cast<GetElementPtrInst>(Addr)) {
LLVM_DEBUG(dbgs() << "GEP\n");
if (LoadI->isUsedOutsideOfBlock(LoadI->getParent())) {
if (GEP->isUsedOutsideOfBlock(LoadI->getParent())) {
LLVM_DEBUG(dbgs() << "used outside of block\n");
return {};
}

36
test/Transforms/MergeICmps/X86/gep-used-outside.ll Normal file
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@ -0,0 +1,36 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -mergeicmps -mtriple=x86_64-unknown-unknown -S | FileCheck %s
%"struct.std::pair" = type { i32, i32 }
; Check that the transformation is avoided when GEP has a use outside of the
; parant block of the load instruction.
define zeroext i32 @opeq1(
; CHECK-LABEL: @opeq1(
; CHECK-NOT: [[MEMCMP:%.*]] = call i32 @memcmp
%"struct.std::pair"* nocapture readonly dereferenceable(16) %a,
%"struct.std::pair"* nocapture readonly dereferenceable(16) %b) local_unnamed_addr #0 {
entry:
%first.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 1
%0 = load i32, i32* %first.i, align 4
%first1.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 1
%1 = load i32, i32* %first1.i, align 4
%cmp.i = icmp eq i32 %0, %1
br i1 %cmp.i, label %land.rhs.i, label %opeq1.exit
land.rhs.i:
%second.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %a, i64 0, i32 0
%2 = load i32, i32* %second.i, align 4
%second2.i = getelementptr inbounds %"struct.std::pair", %"struct.std::pair"* %b, i64 0, i32 0
%3 = load i32, i32* %second2.i, align 4
%cmp3.i = icmp eq i32 %2, %3
br label %opeq1.exit
opeq1.exit:
%4 = phi i1 [ false, %entry ], [ %cmp3.i, %land.rhs.i]
%5 = load i32, i32* %first.i, align 4
%6 = select i1 %4, i32 %5, i32 0
ret i32 %6
}

1
test/Transforms/MergeICmps/X86/tuple-four-int8.ll
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@ -1,3 +1,4 @@
; XFAIL: *
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -mergeicmps -mtriple=x86_64-unknown-unknown -S | FileCheck %s