https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89954
Bug ID: 89954
Summary: missed optimization for signed extension for x86-64
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: ntysdd at qq dot com
Target Milestone: ---
This code snippet
/////////////////////
char c;
int f()
{
return c ^ 1;
}
/////////////////////
is compiled into these instructions with options "-O2 -S"
;;;;;;;;;;;;;;;;;;;;;
movq _c@GOTPCREL(%rip), %rax
movzbl (%rax), %eax
xorl $1, %eax
movsbl %al, %eax
;;;;;;;;;;;;;;;;;;;;;
Only movsbl is needed because xor by 1 doesn't change high bits.
