diff options
| author | Richard Biener <rguenther@suse.de> | 2023-08-04 11:24:49 +0200 |
|---|---|---|
| committer | Richard Biener <rguenther@suse.de> | 2023-08-04 12:16:00 +0200 |
| commit | 04aa0edcace22a7815cfc57575f1f7b1f166ac10 (patch) | |
| tree | ac6c2802b041b72eb25d191e7b488a4d72f37f5a /gcc | |
| parent | 2d2f090e67b26457596e7d5aabe629e3da58db94 (diff) | |
| download | gcc-04aa0edcace22a7815cfc57575f1f7b1f166ac10.zip gcc-04aa0edcace22a7815cfc57575f1f7b1f166ac10.tar.gz gcc-04aa0edcace22a7815cfc57575f1f7b1f166ac10.tar.bz2 | |
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.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/match.pd | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/gcc/match.pd b/gcc/match.pd index aa49574..2278029 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -1081,6 +1081,10 @@ 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))) |