[PATCH] D109419: [GlobalISel] Implement merging of stores of truncates.

[Amara Emerson via Phabricator via llvm-commits]

aemerson created this revision.
aemerson added reviewers: paquette, arsenm, foad.
aemerson added a project: LLVM.
Herald added subscribers: hiraditya, kristof.beyls, rovka.
aemerson requested review of this revision.
Herald added a subscriber: wdng.

This is a port of a combine which matches a pattern where a wide type scalar value is stored by several narrow stores. It folds it into a single store or a BSWAP and a store if the targets supports it.

Assuming little endian target:

   i8 *p = ...
   i32 val = ...
   p[0] = (val >> 0) & 0xFF;
   p[1] = (val >> 8) & 0xFF;
   p[2] = (val >> 16) & 0xFF;
   p[3] = (val >> 24) & 0xFF;
  =>
   *((i32)p) = val;

On CTMark AArch64 -Os this results in a good amount of savings:

  Program            before        after       diff
               SPASS 412792       412788       -0.0%
                  kc 432528       432512       -0.0%
              lencod 430112       430096       -0.0%
    consumer-typeset 419156       419128       -0.0%
              bullet 475840       475752       -0.0%
          tramp3d-v4 367760       367628       -0.0%
            clamscan 383388       383204       -0.0%
      pairlocalalign 249764       249476       -0.1%
      7zip-benchmark 570100       568860       -0.2%
             sqlite3 287628       286920       -0.2%
  Geomean difference                           -0.1%


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D109419

Files:
  llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
  llvm/include/llvm/Target/GlobalISel/Combine.td
  llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
  llvm/test/CodeGen/AArch64/GlobalISel/merge-stores-truncating.ll
  llvm/test/CodeGen/AArch64/GlobalISel/merge-stores-truncating.mir

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