https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113422
Bug ID: 113422
Summary: Missed optimizations in the presence of pointer chains
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: carnet at student dot ethz.ch
Target Milestone: ---
https://godbolt.org/z/hdWKn4bjc
All three functions write to the same variable (b). Clang is able to optimize
this. GCC -O3 cannot always do this.
Assembly for foo is writing to **d instead to directly write 1 to b. There is
similar behavior for bar and baz. Clang optimizes the code to directly write to
b.
Baz is fully optimized only if the foo and bar are removed.
int b = 0;
static int *c = &b;
static int **d = &c;
static int ***e = &d;
void foo() {***e = 1;}
void bar() {**d = 1;}
void baz() {*c = 1;}
Assembly code:
foo:
movq d(%rip), %rax
movq (%rax), %rax
movl $1, (%rax)
ret
