https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118235
Bug ID: 118235
Summary: generate strange code to access const, but not static
array with doubles via index
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dushistov at mail dot ru
Target Milestone: ---
Online demo available here https://godbolt.org/z/6jdKK1K7n .
For code like this:
```
enum class MyEnum { A, B, C, D };
double f(MyEnum mode)
{
const double factors[] = { 2.0, 1.5, 0.5, 0.67 };
return factors[static_cast<unsigned int>(mode)];
}
```
gcc (trunk and all previous versions) on x86-64 generates really strange code:
```
f(MyEnum):
movapd xmm0, XMMWORD PTR .LC0[rip]
mov edi, edi
movaps XMMWORD PTR [rsp-40], xmm0
movapd xmm0, XMMWORD PTR .LC1[rip]
movaps XMMWORD PTR [rsp-24], xmm0
movsd xmm0, QWORD PTR [rsp-40+rdi*8]
ret
.LC0:
.long 0
.long 1073741824
.long 0
.long 1073217536
.LC1:
.long 0
.long 1071644672
.long -687194767
.long 1072001187
```
while clang generates:
```
f(MyEnum):
mov eax, edi
lea rcx, [rip + .L__const.f(MyEnum).factors]
movsd xmm0, qword ptr [rcx + 8*rax]
ret
.L__const.f(MyEnum).factors:
.quad 0x4000000000000000
.quad 0x3ff8000000000000
.quad 0x3fe0000000000000
.quad 0x3fe570a3d70a3d71
```
gcc generates almost the same code as clang if mark `factors` array with
`static` keyword.
