https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114921
Bug ID: 114921
Summary: Optimization flags cause _Float16 to __bf16 casting to
do nothing
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: mat.mcroci at gmail dot com
Target Milestone: ---
When compiling the following code (assuming it's in a file called test.cpp)
#include <stdlib.h>
#include <cstdint>
#include <array>
#include <iostream>
#define SIZE 8
typedef _Float16 T;
//typedef volatile float T;
void fp16tobf16(_Float16 * f) {
__bf16 * b = reinterpret_cast<__bf16*>(f);
for(int i=0; i<SIZE; i++){
T temp = f[i];
b[i] = (__bf16) temp;
}
}
with:
g++ -c -S -O2 -std=c++23 -o test.s test.cpp
using gcc 13.2.0 compiled with binutils 2.42 using spack, the assembler does
not do any casting and simply returns. You can also check this behaviour on
godbolt. The resulting assembly code is simply
fp16tobf16(_Float16*):
ret
When using -O1 or -O0, the assembler generates the command __extendhfbf2 which
causes a separate issue, which is related to this bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114907
P.s. I reported this bug in binutils already, but they suggested I reported it
here instead, see
https://sourceware.org/bugzilla/show_bug.cgi?id=31685
