https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121674
Bug ID: 121674
Summary: X ? C1 : C2 not optimized to (C1 - C2) + C1 * X for С1
> C2
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: antoshkka at gmail dot com
Target Milestone: ---
Consider the example:
int test0(bool cond) { return cond ? 10 : 2; }
GCC now generates the assembly:
"test0(bool)":
cmp dil, 1
sbb eax, eax
and eax, -8
add eax, 10
ret
However a more optimal assembly can be generated:
test0(bool):
lea eax, [8*rdi + 2]
ret
Godbolt playground: https://godbolt.org/z/cGPhxx1Pv
More examples:
int test1(bool cond) { return cond ? 34 : 2; }
int test2(bool cond) { return cond ? 8 : 0; }
int test3(bool cond) { return cond ? 9 : 0; }
int test4(bool cond) { return !cond ? 0 : 9; }
and more optimal assemblies:
test1(bool):
shl edi, 5
lea eax, [rdi + 2]
ret
test2(bool):
lea eax, [8*rdi]
ret
test3(bool):
lea eax, [rdi + 8*rdi]
ret
test4(bool):
lea eax, [rdi + 8*rdi]
ret
