[InstCombine] Improve transforms for `(mul X, Y)` -> `(shl X, log2(Y)`
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Authored by goldstein.w.n on Fri, Mar 17, 7:04 PM.

Details

Reviewers

nikic
spatel
majnemer

Summary

Using the more robust log2 search allows us to fold more cases (same
logic as exists for idiv/irem).

Diff Detail

Repository: rG LLVM Github Monorepo

Unit TestsFailed
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	Time	Test
	110 ms	x64 debian > Flang.Driver::code-gen-rv64.f90 Script: -- : 'RUN: at line 5'; rm -f /var/lib/buildkite-agent/builds/llvm-project/build/tools/flang/test/Driver/Output/code-gen-rv64.f90.tmp.o

Event Timeline

goldstein.w.n created this revision.Fri, Mar 17, 7:04 PM

Herald added a project: Restricted Project. · View Herald TranscriptFri, Mar 17, 7:04 PM

Herald added a subscriber: hiraditya. · View Herald Transcript

goldstein.w.n requested review of this revision.Fri, Mar 17, 7:04 PM

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Harbormaster completed remote builds in B220191: Diff 506257.Fri, Mar 17, 7:05 PM

goldstein.w.n added a parent revision: D146346: [InstCombine] Add tests for indirect mul by power of 2; NFC.Fri, Mar 17, 7:05 PM

goldstein.w.n added reviewers: nikic, spatel, majnemer.

Herald added a subscriber: StephenFan. · View Herald TranscriptFri, Mar 17, 7:06 PM

goldstein.w.n added a child revision: D146349: [InstCombine] Make `FoldOpIntoSelect` handle non-constants and use condition to deduce constants..Fri, Mar 17, 7:06 PM

nikic added inline comments.Sat, Mar 18, 4:53 AM

llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
489	We should preserve the nuw flag here: https://alive2.llvm.org/ce/z/YkwtoD We can't preserve nsw due to the INT_MIN edge case: https://alive2.llvm.org/ce/z/HTaC3b

Rebase

Propegate nuw flag

goldstein.w.n marked an inline comment as done.Sat, Mar 18, 2:01 PM

goldstein.w.n added inline comments.

llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
489	We should preserve the nuw flag here: https://alive2.llvm.org/ce/z/YkwtoD We can't preserve nsw due to the INT_MIN edge case: https://alive2.llvm.org/ce/z/HTaC3b Also added test this.

LGTM

This revision is now accepted and ready to land.Sat, Mar 18, 2:18 PM

Harbormaster completed remote builds in B220249: Diff 506328.Sat, Mar 18, 2:35 PM

Revision Contents
Changeset List

Path

Size

llvm/

lib/

Transforms/

InstCombine/

InstCombineMulDivRem.cpp

23 lines

test/

Transforms/

InstCombine/

mul-pow2.ll

28 lines

Diff 506328

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llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp