[all-commits] [llvm/llvm-project] 600f2e: [X86] Remove SETB_C8r/SETB_C16r pseudo instruction...

[topperc via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 600f2e1c4de59a48a765d9ac8eadab2f4307fa30
      https://github.com/llvm/llvm-project/commit/600f2e1c4de59a48a765d9ac8eadab2f4307fa30
  Author: Craig Topper <craig.topper at intel.com>
  Date:   2020-02-06 (Thu, 06 Feb 2020)

  Changed paths:
    M llvm/lib/Target/X86/X86FlagsCopyLowering.cpp
    M llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
    M llvm/lib/Target/X86/X86InstrCompiler.td
    M llvm/lib/Target/X86/X86InstrInfo.cpp
    M llvm/test/CodeGen/X86/2010-08-04-MaskedSignedCompare.ll
    M llvm/test/CodeGen/X86/flags-copy-lowering.mir
    M llvm/test/CodeGen/X86/sbb.ll
    M llvm/test/CodeGen/X86/vector-compare-any_of.ll

  Log Message:
  -----------
  [X86] Remove SETB_C8r/SETB_C16r pseudo instructions. Use SETB_C32r and EXTRACT_SUBREG instead.

Only 32 and 64 bit SBB are dependency breaking instructons on some
CPUs. The 8 and 16 bit forms have to preserve upper bits of the GPR.

This patch removes the smaller forms and selects the wider form
instead. I had to do this with custom code as the tblgen generated
code glued the eflags copytoreg to the extract_subreg instead of
to the SETB pseudo.

Longer term I think we can remove X86ISD::SETCC_CARRY and use
(X86ISD::SBB zero, zero). We'll want to keep the pseudo and select
(X86ISD::SBB zero, zero) to either a MOV32r0+SBB for targets where
there is no dependency break and SETB_C32/SETB_C64 for targets
that have a dependency break. May want some way to avoid the MOV32r0
if the instruction that produced the carry flag happened to def a
register that we can use for the dependency.

I think the flag copy lowering should be using NEG instead of SUB to
handle SETB. That would avoid the MOV32r0 there. Or maybe it should
use a ADC with -1 to recreate the carry flag and keep the SETB?
That would avoid a MOVZX on the input of the SUB.

Differential Revision: https://reviews.llvm.org/D74024