| Issue |
64241
|
| Summary |
Clang MIPS: float register constraints for inline asm deviate from gcc
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
shravanrn
|
clang and gcc seem to have different behavior of floating point constraints for inline asm. Consider this simple example
```c
// gcc compiles this but clang does not
void read_float(float* p) {
float result = *p;
__asm__("" ::"r"(result));
}
```
The following code compiles fine on gcc when targeting MIPS, but clang gives a compile error `couldn't allocate input reg for constraint 'r'`
Clang requires the register constraint here to be `"f"` not `"r"`. However applying an `"f"` constraint, causes gcc to fail compilation with the error `error: impossible constraint in 'asm'` while clang compiles the code fine.
```c
// clang compiles this but gcc does not
void read_float(float* p) {
float result = *p;
__asm__("" ::"f"(result));
}
```
Here is a simple demo of the issue: https://godbolt.org/z/WGWxd3ejo
Test with "mips gcc 13.1.0" and "mips clang 16.0.0"
(This bug was discovered as part of the wasm2c project https://github.com/WebAssembly/wabt/issues/2266)
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