https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85611
Bug ID: 85611
Summary: Suboptimal code generation for (potentially) redundant
atomic loads
Product: gcc
Version: tree-ssa
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: hiraditya at msn dot com
Target Milestone: ---
$ cat test.cpp
#include <atomic>
std::atomic<int> atomic_var{100};
int somevar;
bool cond;
void run1() {
auto a = atomic_var.load(std::memory_order_relaxed);
auto b = atomic_var.load(std::memory_order_relaxed);
// Some code using a and b;
}
void run2() {
if (atomic_var.load(std::memory_order_relaxed) == 2 && cond) {
if (atomic_var.load(std::memory_order_relaxed) * somevar > 3) {
/*...*/
}
}
}
$ g++-7 -O3 -std=c++17 -S -o - test.cpp -fno-exceptions
.text
.align 4,0x90
.globl __Z4run1v
__Z4run1v:
LFB339:
movl _atomic_var(%rip), %eax
movl _atomic_var(%rip), %eax
ret
LFE339:
.align 4,0x90
.globl __Z4run2v
__Z4run2v:
LFB340:
movl _atomic_var(%rip), %eax
cmpl $2, %eax
je L5
L3:
ret
.align 4,0x90
L5:
cmpb $0, _cond(%rip)
je L3
movl _atomic_var(%rip), %eax
ret
