[gcc(refs/users/marxin/heads/marxin-gcc-benchmark-branch)] rtlanal: optimize costly division in rtx_cost

[gcc(refs/users/marxin/heads/marxin-gcc-benchmark-branch)] rtlanal: optimize costly division in rtx_cost

[Martin Liska]

https://gcc.gnu.org/g:d8305a03b4f0bb081dd9c88917cc8c48def22a80

commit d8305a03b4f0bb081dd9c88917cc8c48def22a80
Author: Alexander Monakov <amonakov@ispras.ru>
Date:   Fri Feb 14 20:14:36 2020 +0300

    rtlanal: optimize costly division in rtx_cost
    
    There's a costly signed 64-bit division in rtx_cost on x86 as well as
    any other target where UNITS_PER_WORD expands to TARGET_64BIT ?  8 : 4.
    It's also evident that rtx_cost does redundant work for a SET.
    
    Obviously the variable named 'factor' rarely exceeds 1, so in the
    majority of cases it can be computed with a well-predictable branch
    rather than a division.
    
    This patch makes rtx_cost do the division only in case mode is wider
    than UNITS_PER_WORD, and also moves a test for a SET up front to avoid
    redundancy.
    No functional change.
    
            * rtlanal.c (rtx_cost): Handle a SET up front. Avoid division if
            the mode is not wider than UNITS_PER_WORD.

Diff:
---
 gcc/ChangeLog |  5 +++++
 gcc/rtlanal.c | 21 +++++++++------------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 1cdec0b4071..2080b738fb6 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2020-02-14  Alexander Monakov  <amonakov@ispras.ru>
+
+	* rtlanal.c (rtx_cost): Handle a SET up front. Avoid division if
+	the mode is not wider than UNITS_PER_WORD.
+
 2020-02-14  Martin Jambor  <mjambor@suse.cz>
 
 	PR tree-optimization/93516
diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c
index 9a7afccefb8..c7ab86e228b 100644
--- a/gcc/rtlanal.c
+++ b/gcc/rtlanal.c
@@ -4207,18 +4207,23 @@ rtx_cost (rtx x, machine_mode mode, enum rtx_code outer_code,
   const char *fmt;
   int total;
   int factor;
+  unsigned mode_size;
 
   if (x == 0)
     return 0;
 
-  if (GET_MODE (x) != VOIDmode)
+  if (GET_CODE (x) == SET)
+    /* A SET doesn't have a mode, so let's look at the SET_DEST to get
+       the mode for the factor.  */
+    mode = GET_MODE (SET_DEST (x));
+  else if (GET_MODE (x) != VOIDmode)
     mode = GET_MODE (x);
 
+  mode_size = estimated_poly_value (GET_MODE_SIZE (mode));
+
   /* A size N times larger than UNITS_PER_WORD likely needs N times as
      many insns, taking N times as long.  */
-  factor = estimated_poly_value (GET_MODE_SIZE (mode)) / UNITS_PER_WORD;
-  if (factor == 0)
-    factor = 1;
+  factor = mode_size > UNITS_PER_WORD ? mode_size / UNITS_PER_WORD : 1;
 
   /* Compute the default costs of certain things.
      Note that targetm.rtx_costs can override the defaults.  */
@@ -4243,14 +4248,6 @@ rtx_cost (rtx x, machine_mode mode, enum rtx_code outer_code,
       /* Used in combine.c as a marker.  */
       total = 0;
       break;
-    case SET:
-      /* A SET doesn't have a mode, so let's look at the SET_DEST to get
-	 the mode for the factor.  */
-      mode = GET_MODE (SET_DEST (x));
-      factor = estimated_poly_value (GET_MODE_SIZE (mode)) / UNITS_PER_WORD;
-      if (factor == 0)
-	factor = 1;
-      /* FALLTHRU */
     default:
       total = factor * COSTS_N_INSNS (1);
     }