https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104405
Bug ID: 104405
Summary: Inefficient register allocation on complex arithmetic
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: tnfchris at gcc dot gnu.org
Target Milestone: ---
The following testcase
#include <complex.h>
complex double f (complex double a, complex double b)
{
return a * b * I;
}
compiled at -Ofast has unneeded copies of input
i.e.
f:
fmov d4, d1
fmov d1, d0
fmul d0, d4, d2
fmul d4, d4, d3
fnmadd d0, d1, d3, d0
fnmsub d1, d1, d2, d4
ret
the first two moves are unneeded and looks to be an artifact of how
IMAGPART_EXPR and REALPART_EXPR are expanded. This seems to be a generic issue
as both x86 and Arm targets seem to have the same problem.
