[PATCH] D135145: [GISel] Combine G_INSERT_VECTOR_ELT to G_SHUFFLE_VECTOR

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


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Comment at: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp:2688-2694
+  SmallVector<int, 4> ShuffleMask;
+  for (unsigned CurIdx = 0; CurIdx < NumElts; ++CurIdx) {
+    if (CurIdx == Idx)
+      ShuffleMask.push_back(NumElts);
+    else
+      ShuffleMask.push_back(CurIdx);
+  }
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There are cases where insert_vector_elts combine to form shuffles but you don't seem to be handling those. This looks like you're just handling basic cases that can use build_vector (which is already implemented in matchCombineInsertVecElts). I'm not following what the shuffles are adding here


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Comment at: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp:2697
+  Builder.buildShuffleVector(Dst, Vec, OtherVec, ShuffleMask);
+  eraseInst(MI);
+}
----------------
I'm not really sure why this eraseInst helper exists


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Comment at: llvm/test/CodeGen/AMDGPU/GlobalISel/combine-insertvecelt-to-shufflevector.mir:2
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -global-isel -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -run-pass=amdgpu-prelegalizer-combiner -verify-machineinstrs -o - %s | FileCheck %s
+# RUN: llc -global-isel -mtriple=amdgcn-amd-amdhsa -mcpu=fiji -run-pass=amdgpu-prelegalizer-combiner -verify-machineinstrs -o - %s | FileCheck %s
----------------
Don't need -global-isel with -run-pass 


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D135145/new/

https://reviews.llvm.org/D135145