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tcg/optimize: prefer the "op a, a, b" form for commutative ops 

The "op a, a, b" form is better handled on non-RISC host than the "op
a, b, a" form, so swap the arguments to this form when possible, and
when b is not a constant.

This reduces the number of generated instructions by a tiny bit.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Aurelien Jarno 2012-09-19 22:00:22 +02:00
parent b336ceb691
commit c2b0e2fea2
1 changed files with 4 additions and 1 deletions
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5
tcg/optimize.c
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@ -434,7 +434,10 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
CASE_OP_32_64(eqv):
CASE_OP_32_64(nand):
CASE_OP_32_64(nor):
if (temps[args[1]].state == TCG_TEMP_CONST) {
/* Prefer the constant in second argument, and then the form
op a, a, b, which is better handled on non-RISC hosts. */
if (temps[args[1]].state == TCG_TEMP_CONST || (args[0] == args[2]
&& temps[args[2]].state != TCG_TEMP_CONST)) {
tmp = args[1];
args[1] = args[2];
args[2] = tmp;