https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115036
Bug ID: 115036
Summary: division is not shortened based on value range
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: hubicka at gcc dot gnu.org
Target Milestone: ---
For
long test(long a, long b)
{
if (a > 65535 || a < 0)
__builtin_unreachable ();
if (b > 65535 || b < 0)
__builtin_unreachable ();
return a/b;
}
we produce
test:
.LFB0:
.cfi_startproc
movq %rdi, %rax
cqto
idivq %rsi
ret
while clang does:
test: # @test
.cfi_startproc
# %bb.0:
movq %rdi, %rax
# kill: def $ax killed $ax killed $rax
xorl %edx, %edx
divw %si
movzwl %ax, %eax
retq
clang also by default adds 32bit divide path even when value range is not known
long test(long a, long b)
{
return a/b;
}
compiles as
test: # @test
.cfi_startproc
# %bb.0:
movq %rdi, %rax
movq %rdi, %rcx
orq %rsi, %rcx
shrq $32, %rcx
je .LBB0_1
# %bb.2:
cqto
idivq %rsi
retq
