Open
Description
Reporting from rust-lang/rust#117970
SimplifyCFG could invert nested switches to reduce code size and number of comparisons
Rust example
extern "Rust" {
fn foo() -> u32;
fn bar() -> u32;
fn baz() -> u32;
}
pub fn src(x: u32, y: u32) -> u32 {
unsafe {
match (x, y) {
(1, 10) => foo(),
(2, 10) => bar(),
(3, 10) => baz(),
_ => 0,
}
}
}
pub fn tgt(x: u32, y: u32) -> u32 {
unsafe {
match (y, x) {
(10, 1) => foo(),
(10, 2) => bar(),
(10, 3) => baz(),
_ => 0,
}
}
}C equivalent
#include <stdint.h>
uint32_t foo();
uint32_t bar();
uint32_t baz();
uint32_t src(uint32_t x, uint32_t y) {
switch (x) {
case 1:
switch (y) {
case 10:
return foo();
default:
return 0;
}
case 2:
switch (y) {
case 10:
return bar();
default:
return 0;
}
case 3:
switch (y) {
case 10:
return baz();
default:
return 0;
}
default:
return 0;
}
}
uint32_t tgt(uint32_t x, uint32_t y) {
switch (y) {
case 10:
switch (x) {
case 1:
return foo();
case 2:
return bar();
case 3:
return baz();
default:
return 0;
}
default:
return 0;
}
}