https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94643
Bug ID: 94643
Summary: [x86_64] gratuitous sign extension of nonnegative
value from 32 to 64 bits
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: bugdal at aerifal dot cx
Target Milestone: ---
Test case:
#include <stdint.h>
uint16_t a[];
uint64_t f(int i)
{
return a[i]*16;
}
Produces:
movslq %edi, %rdi
movzwl a(%rdi,%rdi), %eax
sall $4, %eax
cltq
ret
The value is necessarily in the range [0,1M) (in particular, nonnegative) and
operation on eax has already cleared the upper bits of rax, so cltq is
completely gratuitous. I've observed the same in nontrivial examples where
movslq gets used.
