[PATCH] tree-optimization/91838 - fix FAIL of g++.dg/opt/pr91838.C

[Richard Biener <rguenther@suse.de>]

The following fixes the lack of simplification of a vector shift
by an out-of-bounds shift value.  For scalars this is done both
by CCP and VRP but vectors are not handled there.  This results
in PR91838 differences in outcome dependent on whether a vector
shift ISA is available and thus vector lowering does or does not
expose scalar shifts here.

The following adds a match.pd pattern to catch uniform out-of-bound
shifts, simplifying them to zero when not sanitizing shift amounts.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

OK?

Thanks,
Richard.

	PR tree-optimization/91838
	* match.pd (([rl]shift @0 out-of-bounds) -> zero): New pattern.
---
 gcc/match.pd | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/gcc/match.pd b/gcc/match.pd
index a443dc48634..eace7d635e7 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1059,6 +1059,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
        && tree_nop_conversion_p (type, TREE_TYPE (@1)))
    (lshift @0 @2)))
 
+/* Shifts by precision or greater result in zero.  */
+(for shift (lshift rshift)
+ (simplify
+  (shift @0 uniform_integer_cst_p@1)
+  (if (!(flag_sanitize & SANITIZE_SHIFT_EXPONENT)
+       /* Use a signed compare to leave negative shift counts alone.  */
+       && wi::ges_p (wi::to_wide (uniform_integer_cst_p (@1)),
+		     element_precision (type)))
+   { build_zero_cst (type); })))
+
 /* Shifts by constants distribute over several binary operations,
    hence (X << C) + (Y << C) can be simplified to (X + Y) << C.  */
 (for op (plus minus)
-- 
2.35.3