[all-commits] [llvm/llvm-project] 6d667d: [InstCombine] Combine const GEP chains

[Yingwei Zheng via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6d667d4b261e81f325756fdfd5bb43b3b3d2451d
      https://github.com/llvm/llvm-project/commit/6d667d4b261e81f325756fdfd5bb43b3b3d2451d
  Author: Yingwei Zheng <dtcxzyw2333 at gmail.com>
  Date:   2023-05-02 (Tue, 02 May 2023)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    M llvm/test/Transforms/InstCombine/getelementptr.ll
    M llvm/test/Transforms/LoopVectorize/AArch64/vector-reverse-mask4.ll
    M llvm/test/Transforms/LoopVectorize/consecutive-ptr-uniforms.ll
    M llvm/test/Transforms/LoopVectorize/interleaved-accesses.ll

  Log Message:
  -----------
  [InstCombine] Combine const GEP chains

This patch reverts rGae739aefd7473517d3f08b5c8d08a66c7f469198 to address performance regressions reported by our [CI](https://github.com/dtcxzyw/llvm-ci/issues/137) after rG2ec1d0f427c7822540352c0c14d057e7bfe4f77b.

For example:
```
define ptr @const_gep_chain(ptr %p, i64 %a) {
    %p1 = getelementptr inbounds i8, ptr %p, i64 %a
    %p2 = getelementptr inbounds i8, ptr %p1, i64 1
    %p3 = getelementptr inbounds i8, ptr %p2, i64 2
    %p4 = getelementptr inbounds i8, ptr %p3, i64 3
    ret ptr %p4
}
```
The last three GEPs will not be folded since rG2ec1d0f427c7822540352c0c14d057e7bfe4f77b.

I think it is appropriate to remove this code because there is no compile-time regression reported in our benchmarks.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D149240