https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97690
Bug ID: 97690
Summary: (cond ? 2 : 0) is not optimized to int(cond) << 1
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
enum E { init=0, active=1, done=2 };
int f(bool d)
{
return d ? done : init;
}
int g(bool d)
{
return int(d) << 1;
}
The first function is more readable and less fragile (in case the order of bits
is changed) but GCC produces larger code for it.
For x86_64 with -O3:
f(bool):
xor eax, eax
test dil, dil
setne al
add eax, eax
ret
g(bool):
movzx eax, dil
add eax, eax
ret
And for x86_64 -Os:
f(bool):
neg dil
sbb eax, eax
and eax, 2
ret
g(bool):
movzx eax, dil
add eax, eax
ret
Clang produces the same code for both functions at all optimization levels:
f(bool): # @f(bool)
lea eax, [rdi + rdi]
ret
g(bool): # @g(bool)
lea eax, [rdi + rdi]
ret
