[Bug rtl-optimization/67413] New: Complex NOP expanded to several operations
glisse at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Mon Aug 31 14:43:00 GMT 2015
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67413
Bug ID: 67413
Summary: Complex NOP expanded to several operations
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: glisse at gcc dot gnu.org
Target Milestone: ---
_Complex unsigned f(_Complex int i){return i;}
yields
movl %edi, %eax
shrq $32, %rdi
salq $32, %rdi
orq %rdi, %rax
ret
I read somewhere that complex integers are a deprecated gcc extension, but gcc
only warns in pedantic mode, and it should not be too hard to improve the
generated code.
Note that tree optimizers currently also fail to optimize the corresponding
code:
long f(long x){
long y = x >> 32;
y <<= 32;
int z = x;
return z | y;
}
(using & CST instead of >> and << does not help)
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