[all-commits] [llvm/llvm-project] 17f0c5: [LSR][NFC] Add pre-commit test

[Sergey Kachkov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 17f0c5dfaab8bc72e19cb68e73b0944e5ee27b88
      https://github.com/llvm/llvm-project/commit/17f0c5dfaab8bc72e19cb68e73b0944e5ee27b88
  Author: Sergey Kachkov <sergey.kachkov at syntacore.com>
  Date:   2024-09-09 (Mon, 09 Sep 2024)

  Changed paths:
    A llvm/test/Transforms/LoopStrengthReduce/duplicated-phis.ll

  Log Message:
  -----------
  [LSR][NFC] Add pre-commit test


  Commit: 1f2a634c44dedef11f590956f297b2c7a1659fcf
      https://github.com/llvm/llvm-project/commit/1f2a634c44dedef11f590956f297b2c7a1659fcf
  Author: Sergey Kachkov <sergey.kachkov at syntacore.com>
  Date:   2024-09-09 (Mon, 09 Sep 2024)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
    M llvm/test/Transforms/LoopStrengthReduce/2011-10-03-CritEdgeMerge.ll
    M llvm/test/Transforms/LoopStrengthReduce/AMDGPU/lsr-invalid-ptr-extend.ll
    M llvm/test/Transforms/LoopStrengthReduce/X86/2011-11-29-postincphi.ll
    M llvm/test/Transforms/LoopStrengthReduce/X86/expander-crashes.ll
    M llvm/test/Transforms/LoopStrengthReduce/X86/missing-phi-operand-update.ll
    M llvm/test/Transforms/LoopStrengthReduce/duplicated-phis.ll

  Log Message:
  -----------
  Reland "[LSR] Do not create duplicated PHI nodes while preserving LCSSA form" (#107380)

Motivating example: https://godbolt.org/z/eb97zrxhx
Here we have 2 induction variables in the loop: one is corresponding to
i variable (add rdx, 4), the other - to res (add rax, 2). The second
induction variable can be removed by rewriteLoopExitValues() method
(final value of res at loop exit is unroll_iter * -2); however, this
doesn't happen because we have duplicated LCSSA phi nodes at loop exit:
```
; Preheader:
for.body.preheader.new:                           ; preds = %for.body.preheader
  %unroll_iter = and i64 %N, -4
  br label %for.body

; Loop:
for.body:                                         ; preds = %for.body, %for.body.preheader.new
  %lsr.iv = phi i64 [ %lsr.iv.next, %for.body ], [ 0, %for.body.preheader.new ]
  %i.07 = phi i64 [ 0, %for.body.preheader.new ], [ %inc.3, %for.body ]
  %inc.3 = add nuw i64 %i.07, 4
  %lsr.iv.next = add nsw i64 %lsr.iv, -2
  %niter.ncmp.3.not = icmp eq i64 %unroll_iter, %inc.3
  br i1 %niter.ncmp.3.not, label %for.end.loopexit.unr-lcssa.loopexit, label %for.body, !llvm.loop !7

; Exit blocks
for.end.loopexit.unr-lcssa.loopexit:              ; preds = %for.body
  %inc.3.lcssa = phi i64 [ %inc.3, %for.body ]
  %lsr.iv.next.lcssa11 = phi i64 [ %lsr.iv.next, %for.body ]
  %lsr.iv.next.lcssa = phi i64 [ %lsr.iv.next, %for.body ]
  br label %for.end.loopexit.unr-lcssa
```
rewriteLoopExitValues requires %lsr.iv.next value to have only 2 uses:
one in LCSSA phi node, the other - in induction phi node. Here we have 3
uses of this value because of duplicated lcssa nodes, so the transform
doesn't apply and leads to an extra add operation inside the loop. The
proposed solution is to accumulate inserted instructions that will
require LCSSA form update into SetVector and then call
formLCSSAForInstructions for this SetVector once, so the same
instructions don't process twice.

Reland fixes the issue with preserve-lcssa.ll test: it fails in the situation
when x86_64-unknown-linux-gnu target is unavailable in opt. The changes are
moved into separate duplicated-phis.ll test with explicit x86 target requirement
to fix bots which are not building this target.


Compare: https://github.com/llvm/llvm-project/compare/aa158bf40285...1f2a634c44de

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