[PATCH] D120553: [DAG] SelectionDAG::isSplatValue - add initial BITCAST handling

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: craig.topper, spatel, lebedev.ri, dmgreen.
Herald added subscribers: pengfei, hiraditya.
RKSimon requested review of this revision.
Herald added a project: LLVM.

This patch adds support for recognising vector splats by peeking through bitcasts to vectors with smaller element types - if all the offset subelements are splats then the bitcasted vector is a splat as well.

We don't have great coverage for isSplatValue so I've made this pretty specific to the use case I'm trying to fix - regressions in some vXi64 vector shift by splat cases that 32-bit x86 doesn't recognise because the shift amount buildvector has been type legalised to v2Xi32.

We can add further support (floats, bitcast from larger element types, undef elements) when we have actual test coverage.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D120553

Files:
  llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  llvm/test/CodeGen/X86/pr15296.ll
  llvm/test/CodeGen/X86/vector-fshl-128.ll
  llvm/test/CodeGen/X86/vector-fshl-rot-128.ll
  llvm/test/CodeGen/X86/vector-fshr-128.ll
  llvm/test/CodeGen/X86/vector-fshr-rot-128.ll
  llvm/test/CodeGen/X86/vector-rotate-128.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D120553.411370.patch
Type: text/x-patch
Size: 9898 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220225/473e9442/attachment.bin>