[all-commits] [llvm/llvm-project] c4d3ee: [X86] Fold nested select_cc to select (cmp*ge/le C...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c4d3eedc7f1a954ba3a21af5fc9d4f8ecb37a6ac
      https://github.com/llvm/llvm-project/commit/c4d3eedc7f1a954ba3a21af5fc9d4f8ecb37a6ac
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2021-06-24 (Thu, 24 Jun 2021)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/sdiv_fix_sat.ll
    M llvm/test/CodeGen/X86/udiv_fix_sat.ll

  Log Message:
  -----------
  [X86] Fold nested select_cc to select (cmp*ge/le Cond0, Cond1), LHS, Y)

select (cmpeq Cond0, Cond1), LHS, (select (cmpugt Cond0, Cond1), LHS, Y) --> (select (cmpuge Cond0, Cond1), LHS, Y)
etc,

We already perform this fold in DAGCombiner for MVT::i1 comparison results, but these can still appear after legalization (in x86 case with MVT::i8 results), where we need to be more careful about generating new comparison codes.

Pulled out of D101074 to help address the remaining regressions.

Differential Revision: https://reviews.llvm.org/D104707