https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102169
Bug ID: 102169
Summary: powerpc64 int memory operations using FP instructions
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: npiggin at gmail dot com
CC: bergner at gcc dot gnu.org
Target Milestone: ---
Target: powerpc64le-linux-gnu
--- test.c ---
int foo, bar;
void test(void)
{
foo = bar;
}
---
Using Debian gcc 10.2 with -O2 flag, this compiles to:
addis r2,r12,0
addi r2,r2,0
addis r9,r2,0
addi r9,r9,0
lfiwzx f0,0,r9
addis r9,r2,0
addi r9,r9,0
stfiwx f0,0,r9
blr
Peter confirmed it also uses FP registers with trunk (but I don't have the asm
output at hand).
This can be suboptimal on some processors, e.g., on POWER9 lfiwzx is "Tuple
Restricted (R)" which reduces dispatch throughput on the cycle it is
dispatched. And generally just seems like a surprising thing to do with no
shortage of GPRs.
