[all-commits] [llvm/llvm-project] 547544: [InstSimplify] Allow gep inbounds x, 0 -> x in non...

Nikita Popov via All-commits all-commits at lists.llvm.org
Fri Jul 14 07:17:54 PDT 2023

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 547544112b60da4c6a75210ca4fc6e3bd05914ec
  Author: Nikita Popov <npopov at redhat.com>
  Date:   2023-07-14 (Fri, 14 Jul 2023)

  Changed paths:
    M llvm/lib/Analysis/InstructionSimplify.cpp
    M llvm/test/Transforms/InstCombine/select.ll

  Log Message:
  [InstSimplify] Allow gep inbounds x, 0 -> x in non-refining op replacement

After the semantics change from https://reviews.llvm.org/D154051,
gep inbounds x, 0 can no longer produce poison. As such, we can
also perform this fold during non-refining operand replacement
and avoid unnecessary drops of the inbounds flag.

The online alive2 version has not been update to the new
semantics yet, but we can use the following proof locally:

    define ptr @src(ptr %base, i64 %offset) {
      %cmp = icmp eq i64 %offset, 0
      %gep = getelementptr inbounds i8, ptr %base, i64 %offset
      %sel = select i1 %cmp, ptr %base, ptr %gep
      ret ptr %sel

    define ptr @tgt(ptr %base, i64 %offset) {
      %gep = getelementptr inbounds i8, ptr %base, i64 %offset
      ret ptr %gep

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