[gcc r17-3535] forwprop: Swap the comparisons for the match and the shift amount equality

https://gcc.gnu.org/g:65814ca6027f373806edd21b0125f87359ebdcf2

commit r17-3535-g65814ca6027f373806edd21b0125f87359ebdcf2
Author: Andrea Pinski <[email protected]>
Date:   Fri Aug 21 19:07:46 2026 -0700

    forwprop: Swap the comparisons for the match and the shift amount equality
    
    The current code does:
    ```
      if (gimple_mul_low_sum (sum, sum_ops, NULL)
          && shift_amt == halfwidth)
    ```
    
    But the shift amount check is a much cheaper check than calling
    gimple_mul_low_sum so it should be moved first.
    
    Pushed as obvious after a bootstrapp/test on x86_64-linux-gnu.
    
    gcc/ChangeLog:
    
            * tree-ssa-forwprop.cc (match_long_mul_phi): Swap the shift
            amount check with gimple_mul_low_sum/gimple_mul_cross_sum
            checks.
    
    Signed-off-by: Andrea Pinski <[email protected]>

Diff:
---
 gcc/tree-ssa-forwprop.cc | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 34acbcf033ee..2b832b0041b5 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -4700,8 +4700,8 @@ match_long_mul_phi (gphi *phi)
   unsigned HOST_WIDE_INT halfwidth = TYPE_PRECISION (lhs_type) / 2;
   carry.shift = shift_amt;
 
-  if (gimple_mul_low_sum (sum, sum_ops, NULL)
-      && shift_amt == halfwidth)
+  if (shift_amt == halfwidth
+      && gimple_mul_low_sum (sum, sum_ops, NULL))
     {
       /* mul_carry_low_sum's flat form ties the outer lshift amount to
 	 the inner mul_hi's INTEGER_CST@0 via match.pd capture re-use;
@@ -4713,8 +4713,8 @@ match_long_mul_phi (gphi *phi)
       carry.hilo1 = sum_ops[2];
       carry.hilo2 = sum_ops[3];
     }
-  else if (gimple_mul_cross_sum (sum, sum_ops, NULL)
-	   && shift_amt == halfwidth)
+  else if (shift_amt == halfwidth
+	   && gimple_mul_cross_sum (sum, sum_ops, NULL))
     {
       /* mul_cross_sum is just (plus:c @0 @1) with no half-width
 	 constraint.  Gate here to mirror mul_carry_cross_sum;