The shift isn't necessary. This could have
been re-coded as
return (a-b)<2;
with -fstrict-overflow.
$ cat ga.c
int foo(int a, int b)
{
return (a-b)*4 < 8;
}
$ gcc -S -O2 -fstrict-overflow ga.c
$ cat ga.s
.file "ga.c"
.text
.p2align 4,,15
.globl foo
.type foo, @function
foo:
pushl %ebp
movl %esp, %ebp
movl 8(%ebp), %eax
subl 12(%ebp), %eax
popl %ebp
sall $2, %eax
cmpl $7, %eax
setle %al
movzbl %al, %eax
ret
.size foo, .-foo
.ident "GCC: (GNU) 4.4.0 20090221 (experimental)"
.section .note.GNU-stack,"",@progbits
--
Summary: -fstrict-overflow misses multiply in comparison
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: tkoenig at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39683
