Patchwork [6/9] tcg/optimize: optimize "op r, a, a => movi r, 0"

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Submitter Aurelien Jarno
Date Sept. 19, 2012, 8 p.m.
Message ID <1348084823-18277-7-git-send-email-aurelien@aurel32.net>
Download mbox | patch
Permalink /patch/185208/
State New
Headers show

Comments

Aurelien Jarno - Sept. 19, 2012, 8 p.m.
Now that it's possible to detect copies, we can optimize the case
the "op r, a, a => movi r, 0". This helps the computation of
overflow flags when one of the two args is 0.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
---
 tcg/optimize.c |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)
Richard Henderson - Sept. 19, 2012, 9:46 p.m.
On 09/19/2012 01:00 PM, Aurelien Jarno wrote:
> +        /* Simplify expression for "op r, a, a => movi r, 0" cases */
> +        switch (op) {
> +        CASE_OP_32_64(andc):
> +        CASE_OP_32_64(sub):
> +        CASE_OP_32_64(xor):

For completeness, nand, orc, eqv r, a, a -> -1.

Reviewed-by: Richard Henderson <rth@twiddle.net>


r~

Patch

diff --git a/tcg/optimize.c b/tcg/optimize.c
index cfee690..f8423e0 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -519,6 +519,23 @@  static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
             break;
         }
 
+        /* Simplify expression for "op r, a, a => movi r, 0" cases */
+        switch (op) {
+        CASE_OP_32_64(andc):
+        CASE_OP_32_64(sub):
+        CASE_OP_32_64(xor):
+            if (temps_are_copies(args[1], args[2])) {
+                gen_opc_buf[op_index] = op_to_movi(op);
+                tcg_opt_gen_movi(gen_args, args[0], 0);
+                gen_args += 2;
+                args += 3;
+                continue;
+            }
+            break;
+        default:
+            break;
+        }
+
         /* Propagate constants through copy operations and do constant
            folding.  Constants will be substituted to arguments by register
            allocator where needed and possible.  Also detect copies. */