[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

0 files changed, 0 insertions, 0 deletions