[gcc r12-10294] tree-optimization/110838 - less aggressively fold out-of-bound shifts

[Andre Simoes Dias Vieira]

https://gcc.gnu.org/g:d0eed43ff39a0bad4a02f8af7a4795e06aea6f80

commit r12-10294-gd0eed43ff39a0bad4a02f8af7a4795e06aea6f80
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Aug 4 11:24:49 2023 +0200

    tree-optimization/110838 - less aggressively fold out-of-bound shifts
    
    The following adjusts the shift simplification patterns to avoid
    touching out-of-bound shift value arithmetic right shifts of
    possibly negative values.  While simplifying those to zero isn't
    wrong it's violating the principle of least surprise.
    
            PR tree-optimization/110838
            * match.pd (([rl]shift @0 out-of-bounds) -> zero): Restrict
            the arithmetic right-shift case to non-negative operands.
    
    (cherry picked from commit 04aa0edcace22a7815cfc57575f1f7b1f166ac10)

Diff:
---
 gcc/match.pd | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/match.pd b/gcc/match.pd
index 843b939fc34..c5a4426e76b 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -909,6 +909,10 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (simplify
   (shift @0 uniform_integer_cst_p@1)
   (if ((GIMPLE || !sanitize_flags_p (SANITIZE_SHIFT_EXPONENT))
+       /* Leave arithmetic right shifts of possibly negative values alone.  */
+       && (TYPE_UNSIGNED (type)
+           || shift == LSHIFT_EXPR
+	   || tree_expr_nonnegative_p (@0))
        /* Use a signed compare to leave negative shift counts alone.  */
        && wi::ges_p (wi::to_wide (uniform_integer_cst_p (@1)),
 		     element_precision (type)))