Fix mismatched precisions in tree arithmetic

The tree wi:: decompose routine wasn't asserting that the requested
precision matched the tree's precision.  This could make a difference
for unsigned trees that are exactly N HWIs wide and that have the upper
bit set, since we then need an extra zero HWI when extending it to wider
precisions (as for wi::to_widest).

This patch adds the assert and fixes the fallout shown by the testsuite.
Go seems to be unaffected.

2017-10-02  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree.h (wi::int_traits <const_tree>::decompose): Assert that the
	requested precision matches the type's.
	* calls.c (alloc_max_size): Calculate the new candidate size as
	a widest_int and use wi::to_widest when comparing it with the
	current candidate size.
	* gimple-ssa-warn-alloca.c (pass_walloca::execute): Compare with
	zero rather than integer_zero_node.
	* match.pd: Check for a no-op conversion before using wi::add
	rather than after.  Use tree_to_uhwi when summing small shift
	counts into an unsigned int.

gcc/c-family/
	* c-warn.c (warn_tautological_bitwise_comparison): Use wi::to_widest
	when combining the original unconverted comparison operands.

gcc/cp/
	* constexpr.c (cxx_eval_store_expression): Use wi::to_widest
	when comparing the array bounds with an ARRAY_REF index.

gcc/ada/
	* gcc-interface/decl.c (annotate_value): Use wi::to_widest when
	handling the form (plus/mult (convert @0) @1).

From-SVN: r253341

1 files changed, 2 insertions, 3 deletions

diff --git a/gcc/calls.c b/gcc/calls.c
index 6bd025e..72cf9e0 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -1252,9 +1252,8 @@ alloc_max_size (void)
 
 	      if (unit)
 		{
-		  wide_int w = wi::uhwi (limit, HOST_BITS_PER_WIDE_INT + 64);
-		  w *= unit;
-		  if (wi::ltu_p (w, alloc_object_size_limit))
+		  widest_int w = wi::mul (limit, unit);
+		  if (w < wi::to_widest (alloc_object_size_limit))
 		    alloc_object_size_limit = wide_int_to_tree (ssizetype, w);
 		}
 	    }