[PATCH] D97835: [AArch64][GlobalISel] Add combine for extract_vector_elt(build_vector, cst)

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp:3665-3668
+  MachineInstr *BuildVecMI =
+      getOpcodeDef(TargetOpcode::G_BUILD_VECTOR, SrcVec, MRI);
+  if (!BuildVecMI)
+    return false;
----------------
What about G_BUILD_VECTOR_TRUNC?

This also probably should check for legality / before legalize. The DAG version also has this hasOneUseCheck:

```
      (VecOp.hasOneUse() || TLI.aggressivelyPreferBuildVectorSources(VecVT))) {
```



================
Comment at: llvm/test/CodeGen/AArch64/GlobalISel/combine-extract-vec-elt.mir:25
+    %arg2:_(s64) = COPY $x1
+    %zero:_(s32) = G_CONSTANT i32 0
+    %ins2:_(<2 x s64>) = G_BUILD_VECTOR %arg1(s64), %arg2(s64)
----------------
Should also have an out of bounds case


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D97835/new/

https://reviews.llvm.org/D97835