dyung wrote:
Hi, we have an internal test that checks that compiling with and without
optnone at O0 does not change the code generated by the compiler, and one of
the tests we have did change which I bisected back to your change.
The test consists of the following code:
```c++
#include <math.h>
extern int printf(const char *format, ...);
template <typename T> OPTNONE T &pi(int num_terms) {
static T approx = 0;
for (int i = 0; i <= num_terms; ++i) {
approx += 4 * (pow(-1, i) / ((2 * i) + 1));
}
return approx;
}
OPTNONE
int main() {
int const num_terms = 5;
float f1000 = pi<float>(num_terms);
printf("%f\n", f1000);
return 0;
}
```
When compiled with `-S -O0 -mavx -DOPTNONE=` part of the function
pi<float>(int) looks like this:
```assembly
vcvtsi2sd xmm1, xmm1, eax
vdivsd xmm0, xmm0, xmm1
vmovss xmm2, dword ptr [rip + pi<float>(int)::approx] # xmm2 =
mem[0],zero,zero,zero
vcvtss2sd xmm1, xmm1, xmm2
vmovsd xmm2, qword ptr [rip + .LCPI1_0] # xmm2 = [4.0E+0,0.0E+0]
vmulsd xmm0, xmm0, xmm2
vaddsd xmm1, xmm0, xmm1
vcvtsd2ss xmm0, xmm0, xmm1
vmovss dword ptr [rip + pi<float>(int)::approx], xmm0
```
When compiled with `-S -O0 -mavx -DOPTNONE=__attribute__((optnone))`, the same
code for pi<float>(int) is slightly different:
```assembly
vcvtsi2sd xmm1, xmm1, eax
vdivsd xmm1, xmm0, xmm1
vmovsd xmm0, qword ptr [rip + .LCPI1_0] # xmm0 = [4.0E+0,0.0E+0]
vmulsd xmm1, xmm0, xmm1
vmovss xmm2, dword ptr [rip + pi<float>(int)::approx] # xmm2 =
mem[0],zero,zero,zero
vcvtss2sd xmm0, xmm0, xmm2
vaddsd xmm1, xmm0, xmm1
vcvtsd2ss xmm0, xmm0, xmm1
vmovss dword ptr [rip + pi<float>(int)::approx], xmm0
```
You can see this change on godbolt here: https://godbolt.org/z/WTWPoqY51
Is this change intended?
https://github.com/llvm/llvm-project/pull/85605
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