[gcc r13-35] tree-optimization/105431 - another overflow in powi handling

[Richard Biener]

https://gcc.gnu.org/g:44b09adb9bad99dd7e3017c5ecefed7f7c9a1590

commit r13-35-g44b09adb9bad99dd7e3017c5ecefed7f7c9a1590
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Apr 29 08:45:48 2022 +0200

    tree-optimization/105431 - another overflow in powi handling
    
    This avoids undefined signed overflow when calling powi_as_mults_1.
    
    2022-04-29  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/105431
            * tree-ssa-math-opts.cc (powi_as_mults_1): Make n unsigned.
            (powi_as_mults): Use absu_hwi.
            (gimple_expand_builtin_powi): Remove now pointless n != -n
            check.

Diff:
---
 gcc/tree-ssa-math-opts.cc | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index b528b0523ff..2085597447e 100644
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -1495,7 +1495,7 @@ powi_cost (HOST_WIDE_INT n)
 
 static tree
 powi_as_mults_1 (gimple_stmt_iterator *gsi, location_t loc, tree type,
-		 HOST_WIDE_INT n, tree *cache)
+		 unsigned HOST_WIDE_INT n, tree *cache)
 {
   tree op0, op1, ssa_target;
   unsigned HOST_WIDE_INT digit;
@@ -1548,7 +1548,7 @@ powi_as_mults (gimple_stmt_iterator *gsi, location_t loc,
   memset (cache, 0, sizeof (cache));
   cache[1] = arg0;
 
-  result = powi_as_mults_1 (gsi, loc, type, (n < 0) ? -n : n, cache);
+  result = powi_as_mults_1 (gsi, loc, type, absu_hwi (n), cache);
   if (n >= 0)
     return result;
 
@@ -1572,11 +1572,9 @@ static tree
 gimple_expand_builtin_powi (gimple_stmt_iterator *gsi, location_t loc, 
 			    tree arg0, HOST_WIDE_INT n)
 {
-  /* Avoid largest negative number.  */
-  if (n != -n
-      && ((n >= -1 && n <= 2)
-	  || (optimize_function_for_speed_p (cfun)
-	      && powi_cost (n) <= POWI_MAX_MULTS)))
+  if ((n >= -1 && n <= 2)
+      || (optimize_function_for_speed_p (cfun)
+	  && powi_cost (n) <= POWI_MAX_MULTS))
     return powi_as_mults (gsi, loc, arg0, n);
 
   return NULL_TREE;