https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84151
Bug ID: 84151
Summary: [4.9/5/6/7 Regression] g++ generates two identical
loads in a volatile-qualified member function.
Product: gcc
Version: 7.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wasing at mail dot ru
Target Milestone: ---
The g++ generates two identical loads when the "foo" member function is called
in the following test case:
struct A {
static int& bar(int& a) {
return a;
}
int foo() volatile {
int v = c;
return bar(v);
}
int c;
};
A a;
int main() {
a.c = 2;
a.foo();
return 0;
}
The -O2 options is used to get the following assembler:
.file "test_atomic.cpp"
.section .text.startup,"ax",@progbits
.p2align 4,,15
.globl main
.type main, @function
main:
.LFB2:
.cfi_startproc
movl $2, a(%rip)
movl a(%rip), %eax
movl a(%rip), %eax // !!!DUPLICATED
xorl %eax, %eax
ret
.cfi_endproc
.LFE2:
.size main, .-main
.globl a
.bss
.align 4
.type a, @object
.size a, 4
a:
.zero 4
.ident "GCC: (GNU) 7.2.1 20170915 (Red Hat 7.2.1-2)"
.section .note.GNU-stack,"",@progbits
The "movl a(%rip), %eax" line is repeated twice. The
https://godbolt.org/g/yhQtDw reproduces the issue on many versions newer 4.8.
