[gcc r16-3526] tree-optimization/121753 - ICE with pattern breaking reduction constraints

[Richard Biener]

https://gcc.gnu.org/g:edeb5b8258382a58e1ce8e1e79e61386250d42b2

commit r16-3526-gedeb5b8258382a58e1ce8e1e79e61386250d42b2
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Sep 2 10:16:28 2025 +0200

    tree-optimization/121753 - ICE with pattern breaking reduction constraints
    
    The recent change to vect_synth_mult_by_constant missed to handle
    the synth_shift_p case for alg_shift, so we still changed c * 4
    to c + c + c + c.  The following also amends alg_add_t2_m, alg_sub_t2_m,
    alg_add_factor and alg_sub_factor appropriately.
    
            PR tree-optimization/121753
            * tree-vect-patterns.cc (vect_synth_mult_by_constant): Properly
            bail when synth_shift_p and an alg_shift use.  Handle other
            problematic cases.

Diff:
---
 gcc/tree-vect-patterns.cc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 64a49cccc245..d0bf2f9e7990 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -4329,7 +4329,14 @@ vect_synth_mult_by_constant (vec_info *vinfo, tree op, tree val,
 	  case alg_add_t2_m:
 	  case alg_sub_t2_m:
 	    op_uses++;
+	    /* Fallthru.  */
+	  case alg_shift:
+	    if (synth_shift_p && alg.log[i])
+	      return NULL;
 	    break;
+	  case alg_add_factor:
+	  case alg_sub_factor:
+	    return NULL;
 	  default:
 	    break;
 	  }