https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65250
Bug ID: 65250
Summary: [SH] Improve comparisons followed by a negated cstore
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: olegendo at gcc dot gnu.org
Target: sh*-*-*
The following example
bool test (int value)
{
switch(value)
{
case 0:
case 1:
case 2:
return true;
default:
return false;
}
}
with -O2 -m4 compiles to:
mov #2,r1
cmp/hi r1,r4
mov #-1,r0
rts
negc r0,r0
On SH4 there is no movrt, so it's better to do that as:
mov #2,r1
cmp/hs r4,r2
rts
movt r0
..which is just inverting the comparison.
Combine tries the following pattern:
Failed to match this instruction:
(parallel [
(set (reg:SI 168)
(leu:SI (reg:SI 4 r4 [ value ])
(const_int 2 [0x2])))
(set (reg:SI 147 t)
(const_int 1 [0x1]))
(use (reg:SI 169))
])
..which is a combination of the inverted comparison and the expanded movrt (via
negc), which always sets T = 1.
A treg_set_expr pattern like the following could be added:
(define_insn_and_split "*"
[(set (match_operand:SI 0 "arith_reg_dest")
(match_operand 1 "treg_set_expr_not_const01"))
(set (reg:SI T_REG) (const_int 1))
(use (match_operand:SI 2 "arith_reg_operand"))]
...)
which would then split out the comparison insn and a trailing sett. If the
sett is a dead store it will (should) get eliminated afterwards.
However, before that, the initial comparison and cstore expansion should be
investigated.
