[Bug rtl-optimization/98425] Superfluous sign-extend for constrained integer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98425 --- Comment #5 from Nicolas Koenig --- The advantage of using mov over movs for known-positive integers would be that 32bit moves are also move-eliminated, while movs always has to be executed.
[Bug rtl-optimization/98425] Superfluous sign-extend for constrained integer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98425 Jakub Jelinek changed: What|Removed |Added CC||jakub at gcc dot gnu.org --- Comment #4 from Jakub Jelinek --- Sorry, in this case it isn't wrong (that is the passing of char/short case), the __builtin_unreachable () says that negative values are undefined, therefore the compiler can use both sign and zero extension interchangeably. And the undefined signed overflow means when we have: int i; ... ((unsigned long long) (i + 4)) * 4 we can compute it as ((unsigned long long) (i + 4)) * 4 or ((unsigned long long) i) * 4 + 16 because if i is in [INT_MAX - 3, INT_MAX] it is UB.
[Bug rtl-optimization/98425] Superfluous sign-extend for constrained integer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98425 --- Comment #3 from Jakub Jelinek --- Yes, it has been reported to LLVM years ago that they violate the psABI, but they refused to fix that.
[Bug rtl-optimization/98425] Superfluous sign-extend for constrained integer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98425 --- Comment #2 from Andrew Pinski --- Note your optimum code is wrong. movl %esi, %eax Is a zero extend.
[Bug rtl-optimization/98425] Superfluous sign-extend for constrained integer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98425 Andrew Pinski changed: What|Removed |Added Keywords||ABI --- Comment #1 from Andrew Pinski --- Actually this is an abi issue. The upper 32bits of the register is undefined by the x86_64 ABI iirc. If this is true then clang has a bug.
