[PATCH] D28251: [AArch64] Fix over-eager early-exit in load-store combiner

[Chad Rosier via Phabricator via llvm-commits]

mcrosier added a comment.

I think this test case exposes the underlying issue:

  define i64 @test(i64* %a) nounwind {
    %p1 = getelementptr inbounds i64, i64* %a, i32 64
    %tmp1 = load i64, i64* %p1, align 2
    %p2 = getelementptr inbounds i64, i64* %a, i32 63
    %tmp2 = load i64, i64* %p2, align 2
    %tmp3 = add i64 %tmp1, %tmp2
    ret i64 %tmp3
  }

When you run llc make sure to disable the scheduler so that the instructions aren't reordered by using -enable-misched=false and -enable-post-misched=false.

Reproduce with:

  llc -mtriple=aarch64-linux-gnu -aarch64-enable-atomic-cfg-tidy=0 -disable-lsr -verify-machineinstrs -enable-misched=false -enable-post-misched=false -o - test.ll

If I'm not mistaken, without this patch we won't pair the instructions.


https://reviews.llvm.org/D28251