| Issue |
98946
|
| Summary |
function return `range` metadata not inferred from `assume`s
|
| Labels |
missed-optimization
|
| Assignees |
|
| Reporter |
Kmeakin
|
The propagation of range information from `assume` is very fragile.
Things that prevent it from propagating:
- The `assume` is in its own function
- The condition passed to `assume` is extracted into a helper function (eg `is_surrogate`)
- The condition passed to `assume` combines two comparisons with `or`
- The condition passed to `assume` is the negation of another comparison
https://godbolt.org/z/hvdxE1xKn
```c
#include <stdbool.h>
#include <stdint.h>
typedef uint32_t u32;
void assume(bool b) { __builtin_assume(b); }
bool is_surrogate(u32 c) { return 0xD800 <= c && c <= 0xDFFF; }
// range not inferred
u32 f1(u32 c) {
assume(!is_surrogate(c));
return c;
}
// range not inferred
u32 f2(u32 c) {
__builtin_assume(!is_surrogate(c));
return c;
}
// range not inferred
u32 f3(u32 c) {
__builtin_assume(!(0xD800 <= c && c <= 0xDFFF));
return c;
}
// range not inferred
u32 f4(u32 c) {
__builtin_assume(c < 0xD800 || c > 0xDFFF);
return c;
}
// range(i32 0, 55296) inferred
u32 f5(u32 c) {
__builtin_assume(c < 0xD800);
return c;
}
// range(i32 55297, 0) inferred
u32 f6(u32 c) {
__builtin_assume(c > 0xD800);
return c;
}
// range not inferred
u32 f7(u32 c) {
__builtin_assume(!(0xD800 <= c));
return c;
}
// range not inferred
u32 f8(u32 c) {
__builtin_assume(!(c <= 0xDFFF));
return c;
}
```
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