More NEGATE_EXPR folding in match.pd

As observed by Jakub in comment #2 of PR 98865, the expression -(a>>63)
is optimized in GENERIC but not in GIMPLE.  Investigating further it
turns out that this is one of a few transformations performed by
fold_negate_expr in fold-const.c that aren't yet performed by match.pd.
This patch moves/duplicates them there, and should be relatively safe
as these transformations are already performed by the compiler, but
just in different passes.

This revised patch adds a Boolean simplify argument to tree-ssa-sccvn.c's
vn_nary_build_or_lookup_1 to control whether simplification should be
performed before value numbering, updating the callers, but then
avoiding simplification when constructing/value-numbering NEGATE_EXPR.
This avoids the regression of gcc.dg/tree-ssa/ssa-free-88.c, and enables
the new test case(s) to pass.

2021-09-22  Roger Sayle  <roger@nextmovesoftware.com>
	    Richard Biener  <rguenther@suse.de>

gcc/ChangeLog
	* match.pd (negation simplifications): Implement some negation
	folding transformations from fold-const.c's fold_negate_expr.
	* tree-ssa-sccvn.c (vn_nary_build_or_lookup_1): Add a SIMPLIFY
	argument, to control whether the op should be simplified prior
	to looking up/assigning a value number.
	(vn_nary_build_or_lookup): Update call to vn_nary_build_or_lookup_1.
	(vn_nary_simplify): Likewise.
	(visit_nary_op): Likewise, but when constructing a NEGATE_EXPR
	now call vn_nary_build_or_lookup_1 disabling simplification.

gcc/testsuite/ChangeLog
	* gcc.dg/fold-negate-1.c: New test case.

1 files changed, 30 insertions, 0 deletions

diff --git a/gcc/match.pd b/gcc/match.pd
index a063a15..a9791ce 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1481,6 +1481,36 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (if (!FIXED_POINT_TYPE_P (type))
  (plus @0 (negate @1))))
 
+/* Other simplifications of negation (c.f. fold_negate_expr_1).  */
+(simplify
+ (negate (mult:c@0 @1 negate_expr_p@2))
+ (if (! TYPE_UNSIGNED (type)
+      && ! HONOR_SIGN_DEPENDENT_ROUNDING (type)
+      && single_use (@0))
+  (mult @1 (negate @2))))
+
+(simplify
+ (negate (rdiv@0 @1 negate_expr_p@2))
+ (if (! HONOR_SIGN_DEPENDENT_ROUNDING (type)
+      && single_use (@0))
+  (rdiv @1 (negate @2))))
+
+(simplify
+ (negate (rdiv@0 negate_expr_p@1 @2))
+ (if (! HONOR_SIGN_DEPENDENT_ROUNDING (type)
+      && single_use (@0))
+  (rdiv (negate @1) @2)))
+
+/* Fold -((int)x >> (prec - 1)) into (unsigned)x >> (prec - 1).  */
+(simplify
+ (negate (convert? (rshift @0 INTEGER_CST@1)))
+ (if (tree_nop_conversion_p (type, TREE_TYPE (@0))
+      && wi::to_wide (@1) == element_precision (type) - 1)
+  (with { tree stype = TREE_TYPE (@0);
+	  tree ntype = TYPE_UNSIGNED (stype) ? signed_type_for (stype)
+					     : unsigned_type_for (stype); }
+   (convert (rshift:ntype (convert:ntype @0) @1)))))
+
 /* Try to fold (type) X op CST -> (type) (X op ((type-x) CST))
    when profitable.
    For bitwise binary operations apply operand conversions to the