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* [Bug rtl-optimization/111744] New: Missed optimization when casting rdtsc into uint32_t and computing difference
@ 2023-10-09 19:17 stefan.sakalik at gmail dot com
0 siblings, 0 replies; only message in thread
From: stefan.sakalik at gmail dot com @ 2023-10-09 19:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111744
Bug ID: 111744
Summary: Missed optimization when casting rdtsc into uint32_t
and computing difference
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: stefan.sakalik at gmail dot com
Target Milestone: ---
This is similar to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92180 where
this code: https://godbolt.org/z/7W9nqTsjE
#include <bits/stdc++.h>
#include <x86intrin.h>
uint32_t rdtsc32() { return static_cast<uint32_t>(__rdtsc()); }
uint64_t rdtsc_delta(uint64_t x) {
return rdtsc32() - rdtsc32();
}
Produces
rdtsc_delta(unsigned long):
rdtsc
mov rcx, rax
sal rdx, 32
or rcx, rdx
rdtsc
sub ecx, eax
mov rax, rcx
ret
as opposed to clang version
rdtsc_delta(unsigned long):
rdtsc
mov rcx, rax
rdtsc
sub ecx, eax
mov rax, rcx
ret
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2023-10-09 19:17 [Bug rtl-optimization/111744] New: Missed optimization when casting rdtsc into uint32_t and computing difference stefan.sakalik at gmail dot com
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