qemu/0075-tcg-optimize-prefer-the-op-a-a-b-form-for-commutativ.patch
Cole Robinson 9290838132 Fix boot hang if console is not connected (bz #894451)
Fix segfault with zero length virtio-scsi disk (bz #847549)
2013-02-02 15:47:37 -05:00

36 lines
1.4 KiB
Diff

From a0b71ad6a3f8aeb8b5ea6d112a7afeadc7c004a4 Mon Sep 17 00:00:00 2001
From: Aurelien Jarno <aurelien@aurel32.net>
Date: Wed, 19 Sep 2012 22:00:22 +0200
Subject: [PATCH] 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>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
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;