[GlobalISel] Fix DIVREM combine from inserting a divrem before its operands' defs.
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Authored by aemerson on Feb 18 2023, 2:26 PM.

Details

Reviewers

arsenm
cdevadas
paquette

Summary

In some rare corner cases where in between the div/rem pair there's a def of
the second instruction's source (but a different vreg due to the combine's
eqivalence checks), it will place the DIVREM at the first instruction's point,
causing a use-before-def. There wasn't an obvious fix that stood out to me
without doing more involved analysis than a combine should really be doing.

Fixes issue #60516

I'm open to new suggestions on how to approach this, as I'm not too happy
at bailing out here. It's not the first time we run into issues with value liveness
that the DAG world isn't affected by.

Diff Detail

Repository: rG LLVM Github Monorepo

Unit TestsFailed
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	Time	Test
	60,060 ms	x64 debian > MLIR.Examples/standalone::test.toy Script: -- : 'RUN: at line 1'; /usr/bin/cmake /var/lib/buildkite-agent/builds/llvm-project/mlir/examples/standalone -G "Ninja" -DCMAKE_CXX_COMPILER=/usr/bin/clang++ -DCMAKE_C_COMPILER=/usr/bin/clang -DLLVM_ENABLE_LIBCXX=OFF -DMLIR_DIR=/var/lib/buildkite-agent/builds/llvm-project/build/lib/cmake/mlir -DLLVM_USE_LINKER=lld -DPython3_EXECUTABLE="/usr/bin/python3.9"
	60,070 ms	x64 debian > libFuzzer.libFuzzer::fuzzer-leak.test Script: -- : 'RUN: at line 3'; /var/lib/buildkite-agent/builds/llvm-project/build/./bin/clang --driver-mode=g++ -O2 -gline-tables-only -fsanitize=address,fuzzer -I/var/lib/buildkite-agent/builds/llvm-project/compiler-rt/lib/fuzzer -m64 /var/lib/buildkite-agent/builds/llvm-project/compiler-rt/test/fuzzer/LeakTest.cpp -o /var/lib/buildkite-agent/builds/llvm-project/build/projects/compiler-rt/test/fuzzer/X86_64DefaultLinuxConfig/Output/fuzzer-leak.test.tmp-LeakTest
	60,060 ms	x64 debian > libFuzzer.libFuzzer::minimize_crash.test Script: -- : 'RUN: at line 1'; /var/lib/buildkite-agent/builds/llvm-project/build/./bin/clang --driver-mode=g++ -O2 -gline-tables-only -fsanitize=address,fuzzer -I/var/lib/buildkite-agent/builds/llvm-project/compiler-rt/lib/fuzzer -m64 /var/lib/buildkite-agent/builds/llvm-project/compiler-rt/test/fuzzer/NullDerefTest.cpp -o /var/lib/buildkite-agent/builds/llvm-project/build/projects/compiler-rt/test/fuzzer/X86_64DefaultLinuxConfig/Output/minimize_crash.test.tmp-NullDerefTest
	60,060 ms	x64 debian > libFuzzer.libFuzzer::out-of-process-fuzz.test Script: -- : 'RUN: at line 2'; rm -rf /var/lib/buildkite-agent/builds/llvm-project/build/projects/compiler-rt/test/fuzzer/X86_64DefaultLinuxConfig/Output/out-of-process-fuzz.test.tmp && mkdir /var/lib/buildkite-agent/builds/llvm-project/build/projects/compiler-rt/test/fuzzer/X86_64DefaultLinuxConfig/Output/out-of-process-fuzz.test.tmp
	60,070 ms	x64 debian > libFuzzer.libFuzzer::value-profile-load.test Script: -- : 'RUN: at line 2'; /var/lib/buildkite-agent/builds/llvm-project/build/./bin/clang --driver-mode=g++ -O2 -gline-tables-only -fsanitize=address,fuzzer -I/var/lib/buildkite-agent/builds/llvm-project/compiler-rt/lib/fuzzer -m64 /var/lib/buildkite-agent/builds/llvm-project/compiler-rt/test/fuzzer/LoadTest.cpp -fsanitize-coverage=trace-gep -o /var/lib/buildkite-agent/builds/llvm-project/build/projects/compiler-rt/test/fuzzer/X86_64DefaultLinuxConfig/Output/value-profile-load.test.tmp-LoadTest

Event Timeline

aemerson created this revision.Feb 18 2023, 2:26 PM

Herald added a project: Restricted Project. · View Herald TranscriptFeb 18 2023, 2:26 PM

Herald added a subscriber: hiraditya. · View Herald Transcript

aemerson requested review of this revision.Feb 18 2023, 2:26 PM

Herald added a subscriber: wdng. · View Herald TranscriptFeb 18 2023, 2:26 PM

Harbormaster completed remote builds in B214601: Diff 498632.Feb 18 2023, 3:14 PM

This feels way more complicated than necessary but I don't really have a better suggestion

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
1202	This will miss implicit defs if a non-G_* instruction ends up in the middle somehow

Check all defs.

Harbormaster completed remote builds in B214944: Diff 499062.Feb 21 2023, 2:39 AM

ping

Revision Contents
Changeset List

Path

Size

llvm/

lib/

CodeGen/

GlobalISel/

CombinerHelper.cpp

40 lines

test/

CodeGen/

AArch64/

GlobalISel/

prelegalizer-combiner-divrem-insertpt-conflict.mir

121 lines

Diff 499062

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llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp