[all-commits] [llvm/llvm-project] 1e552d: [X86] Improve select of constants

[kazutakahirata via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1e552d0c5bf1627b92ac205cab07d3e09d911750
      https://github.com/llvm/llvm-project/commit/1e552d0c5bf1627b92ac205cab07d3e09d911750
  Author: Kazu Hirata <kazu at google.com>
  Date:   2023-02-28 (Tue, 28 Feb 2023)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/select-constant-xor.ll
    M llvm/test/CodeGen/X86/select_const.ll

  Log Message:
  -----------
  [X86] Improve select of constants

Without this patch:

  %cmp = icmp eq i32 %a, %b
  %cond = select i1 %cmp, i32 1, i32 2

is compiled as:

  31 c9                      xor    %ecx,%ecx
  39 f7                      cmp    %esi,%edi
  0f 94 c1                   sete   %cl
  b8 02 00 00 00             mov    $0x2,%eax
  29 c8                      sub    %ecx,%eax

With this patch, the compiler generates:

  31 c0                      xor    %eax,%eax
  39 f7                      cmp    %esi,%edi
  0f 95 c0                   setne  %al
  ff c0                      inc    %eax

saving 5 bytes while reducing register usage.

This patch transforms C - setcc into inverted_setcc + (C-1) if C is a
nonzero constant.

This patch fixes:

https://github.com/llvm/llvm-project/issues/60854

Differential Revision: https://reviews.llvm.org/D144449