https://bugs.llvm.org/show_bug.cgi?id=51137
Bug ID: 51137
Summary: missed optimization for dead code elimination at -O3
(vs. -O2)
Product: new-bugs
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
$./bin/clang -v
clang version 13.0.0 (https://github.com/llvm/llvm-project.git
96d8f2a1e0842b83b319a8daf3cc82dd5e1350fa)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /dev/shm/llvm-project/build/./bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/10
Candidate multilib: .;@m64
Selected multilib: .;@m64
$cat test.c
extern void foo(void);
extern void bar(void);
int a, b, c, d, f;
int main() {
int e[4] = {0,0,0,0}, g = 0, h, i;
for (; g < 4; g++)
for (h = 0; h < 6; h++)
for (i = 0; i < 9; i++)
bar();
while (d) {
f = e[3] << c;
if (f)
foo();
b = e[a];
}
return 0;
}
$./bin/clang -O2 test.c -S -o O2.s
$./bin/clang -O3 test.c -S -o O3.s
$grep foo O2.s
$grep foo O3.s
callq foo
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