[Qemu-devel] [PATCH v2 08/10] tcg/optimize: prefer the "op a, a, b" form for commutative ops

[Aurelien Jarno <aurelien@aurel32.net>]

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.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
---
 tcg/optimize.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tcg/optimize.c b/tcg/optimize.c
index abe016a..c8ae50b 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -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;
-- 
1.7.10.4