[Bug target/88402] New: inefficient code generation for mask from CC

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88402

            Bug ID: 88402
           Summary: inefficient code generation for mask from CC
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

For sth like

unsigned long foo (int a, int b)
{
  return a < b ? -1ul : 0;
}

we produce at -O[23]

        xorl    %eax, %eax
        cmpl    %esi, %edi
        setl    %al
        negq    %rax
        ret

(partial register stall?)

and at -O

        cmpl    %esi, %edi
        setl    %al
        movzbl  %al, %eax
        negq    %rax

while we could use sbbq %rax, %rax if the suggestion at
https://lwn.net/Articles/744257/ is correct.