Make tree_expr_nonnegative_warnv_p recurse into SSA names

The upcoming patch to move sqrt and cbrt simplifications to match.pd
caused a regression because the (abs @0)->@0 simplification didn't
trigger for:

        (abs (convert (abs X)))

The simplification is based on tree_expr_nonnegative_p, which at
the moment just gives up if it sees an SSA_NAME.

This patch makes tree_expr_nonnegative_p recurse into SSA name
definitions, but limits the depth of recursion to a small number
for the reason mentioned in the comment (adapted from an existing
comment in gimple_val_nonnegative_real_p).  The patch reuses code
in tree-vrp.c, moving it to gimple-fold.c.  It also replaces calls
to gimple_val_nonnegative_real_p with calls to tree_expr_nonnegative_p.

A knock-on effect is that we can now prove _i_589 < 0 is false in
sequences like:

      i_1917 = ASSERT_EXPR <i_1075, i_1075 == 0>;
      _i_589 = (const int) i_1917;
      _i_1507 = ASSERT_EXPR <_i_589, _i_589 < 0>;

This defeats an assert in tree-vrp.c that ASSERT_EXPR conditions
are never known to be false.  Previously the assert only ever used
local knowledge and so would be limited to cases like x != x for
integer x.  Now that we use global knowledge it's possible to prove
the assertion condition is false in blocks that are in practice
unreachable.  The patch therefore removes the assert.

Bootstrapped & regression-tested on x86_64-linux-gnu.  I didn't write
a specific test because this is already covered by the testsuite if
the follow-on patch is also applied.

gcc/
	* params.def (PARAM_MAX_SSA_NAME_QUERY_DEPTH): New param.
	* doc/invoke.texi (--param max-ssa-name-query-depth): Document.
	* fold-const.h (tree_unary_nonnegative_warnv_p)
	(tree_single_nonnegative_warnv_p, tree_call_nonnegative_warnv_p)
	(tree_expr_nonnegative_warnv_p): Add depth parameters.
	* fold-const.c: Include gimple-fold.h and params.h.
	(tree_ssa_name_nonnegative_warnv_p): New function.
	(tree_unary_nonnegative_warnv_p, tree_binary_nonnegative_warnv_p)
	(tree_single_nonnegative_warnv_p, tree_call_nonnegative_warnv_p)
	(tree_invalid_nonnegative_warnv_p, tree_expr_nonnegative_warnv_p):
	Add a depth parameter and increment it for recursive calls to
	tree_expr_nonnegative_warnv_p.  Use tree_ssa_name_nonnegative_warnv_p
	to handle SSA names.
	* gimple-fold.h (gimple_val_nonnegative_real_p): Delete.
	(gimple_stmt_nonnegative_warnv_p): Declare.
	* tree-vrp.c (remove_range_assertions): Remove assert that condition
	cannot be proven false.
	(gimple_assign_nonnegative_warnv_p, gimple_call_nonnegative_warnv_p)
	(gimple_stmt_nonnegative_warnv_p): Move to...
	* gimple-fold.c: ...here.  Add depth parameters and pass them
	down to the tree routines.  Accept statements that aren't
	assignments or calls but just return false for them.
	(gimple_val_nonnegative_real_p): Delete.
	* tree-ssa-math-opts.c (gimple_expand_builtin_pow): Use
	tree_expr_nonnegative_p instead of gimple_val_nonnegative_real_p.
	Check HONOR_NANs first.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@228614 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 7 insertions, 5 deletions

diff --git a/gcc/fold-const.h b/gcc/fold-const.h
index 4a31e62600f..ee74dc87b6b 100644
--- a/gcc/fold-const.h
+++ b/gcc/fold-const.h
@@ -132,11 +132,13 @@ extern bool tree_unary_nonzero_warnv_p (enum tree_code, tree, tree, bool *);
 extern bool tree_binary_nonzero_warnv_p (enum tree_code, tree, tree, tree op1,
                                          bool *);
 extern bool tree_single_nonzero_warnv_p (tree, bool *);
-extern bool tree_unary_nonnegative_warnv_p (enum tree_code, tree, tree, bool *);
+extern bool tree_unary_nonnegative_warnv_p (enum tree_code, tree, tree,
+					    bool *, int);
 extern bool tree_binary_nonnegative_warnv_p (enum tree_code, tree, tree, tree,
-                                             bool *);
-extern bool tree_single_nonnegative_warnv_p (tree t, bool *strict_overflow_p);
-extern bool tree_call_nonnegative_warnv_p (tree, tree, tree, tree, bool *);
+					     bool *, int);
+extern bool tree_single_nonnegative_warnv_p (tree, bool *, int);
+extern bool tree_call_nonnegative_warnv_p (tree, tree, tree, tree, bool *,
+					   int);
 
 extern bool fold_real_zero_addition_p (const_tree, const_tree, int);
 extern tree combine_comparisons (location_t, enum tree_code, enum tree_code,
@@ -160,7 +162,7 @@ extern tree size_diffop_loc (location_t, tree, tree);
 extern tree non_lvalue_loc (location_t, tree);
 
 extern bool tree_expr_nonnegative_p (tree);
-extern bool tree_expr_nonnegative_warnv_p (tree, bool *);
+extern bool tree_expr_nonnegative_warnv_p (tree, bool *, int = 0);
 extern tree make_range (tree, int *, tree *, tree *, bool *);
 extern tree make_range_step (location_t, enum tree_code, tree, tree, tree,
 			     tree *, tree *, int *, bool *);