Patchwork [v2,2/4] tcg/optimize: fix known-zero bits optimization

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Submitter Aurelien Jarno
Date Sept. 9, 2013, 5:27 p.m.
Message ID <1378747670-25512-3-git-send-email-aurelien@aurel32.net>
Download mbox | patch
Permalink /patch/273622/
State New
Headers show

Comments

Aurelien Jarno - Sept. 9, 2013, 5:27 p.m.
Known-zero bits optimization is a great idea that helps to generate more
optimized code. However the current implementation only works in very few
cases as the computed mask is not saved.

Fix this to make it really working.

Cc: Richard Henderson <rth@twiddle.net>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
---
 tcg/optimize.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
Richard Henderson - Dec. 6, 2013, 5:54 p.m.
On 09/10/2013 05:27 AM, Aurelien Jarno wrote:
> Known-zero bits optimization is a great idea that helps to generate more
> optimized code. However the current implementation only works in very few
> cases as the computed mask is not saved.
> 
> Fix this to make it really working.
> 
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
> ---
>  tcg/optimize.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)

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


r~

Patch

diff --git a/tcg/optimize.c b/tcg/optimize.c
index c539e39..0ed8983 100644
--- a/tcg/optimize.c
+++ b/tcg/optimize.c
@@ -695,7 +695,8 @@  static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
             break;
         }
 
-        /* Simplify using known-zero bits */
+        /* Simplify using known-zero bits. Currently only ops with a single
+           output argument is supported. */
         mask = -1;
         affected = -1;
         switch (op) {
@@ -1157,6 +1158,11 @@  static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
             } else {
                 for (i = 0; i < def->nb_oargs; i++) {
                     reset_temp(args[i]);
+                    /* Save the corresponding known-zero bits mask for the
+                       first output argument (only one supported so far). */
+                    if (i == 0) {
+                        temps[args[i]].mask = mask;
+                    }
                 }
             }
             for (i = 0; i < def->nb_args; i++) {