https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66235
Bug ID: 66235
Summary: [SH] Optimize tst reg,const movrt sequence
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: olegendo at gcc dot gnu.org
Target Milestone: ---
Target: sh*-*-*
The following example:
bool test_00 (unsigned int x)
{
return (x & 0x1042A) != 0;
}
compiled with -O2 -m4:
mov.l .L3,r1
tst r1,r4
mov #-1,r1
rts
negc r1,r0
.L4:
.align 2
.L3:
.long 0x1042A
On non-SH2A there is no movrt insn and a !T -> reg move is done via negc. If
the preceeding tst insn uses a constant, the constant can be complemented to
avoid the negc and #-1 constant load:
mov.l .L3,r1
tst r1,r4
rts
movt r0
.L4:
.align 2
.L3:
.long 0xFFFEFBD5
The tstsi_t splitter could be extended to look for a following movrt insn and
optimize it accordingly.
The downside of doing this is an increased constant pool size, if the original
(non-complemented) constant is used for something else. Moreover, it is only
beneficial to do this if there are no other negc #-1 movrt insns which share
the #-1 constant. On the other hand, sharing the #-1 constant increases the
life time of regs and thus increases reg pressure.
