x86: Build only one __cpu_model/__cpu_features2 variables
GCC -O2 generated quite bad code for this function:
bool
f (void)
{
return __builtin_cpu_supports("popcnt")
&& __builtin_cpu_supports("ssse3");
}
f:
movl __cpu_model+12(%rip), %edx
movl %edx, %eax
shrl $6, %eax
andl $1, %eax
andl $4, %edx
movl $0, %edx
cmove %edx, %eax
ret
The problem was caused by the fact that internally every invocation of
__builtin_cpu_supports built a new variable __cpu_model and a new type
__processor_model. Because of this, GIMPLE level optimizers weren't able
to CSE the loads of __cpu_model and optimize bit-operations properly.
Improve GCC -O2 code generation by caching __cpu_model and__cpu_features2
variables as well as their types:
f:
movl __cpu_model+12(%rip), %eax
andl $68, %eax
cmpl $68, %eax
sete %al
ret
2021-05-05 Ivan Sorokin <vanyacpp@gmail.com>
H.J. Lu <hjl.tools@gmail.com>
gcc/
PR target/91400
* config/i386/i386-builtins.c (ix86_cpu_model_type_node): New.
(ix86_cpu_model_var): Likewise.
(ix86_cpu_features2_type_node): Likewise.
(ix86_cpu_features2_var): Likewise.
(fold_builtin_cpu): Cache __cpu_model and __cpu_features2 with
their types.
gcc/testsuite/
PR target/91400
* gcc.target/i386/pr91400-1.c: New test.
* gcc.target/i386/pr91400-2.c: Likewise.