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analyzer: fix handling of negative byte offsets (v2) (PR 93281)

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Various 32-bit targets show failures in gcc.dg/analyzer/data-model-1.c
with tests of the form:
  __analyzer_eval (q[-2].x == 107024); /* { dg-warning "TRUE" } */
  __analyzer_eval (q[-2].y == 107025); /* { dg-warning "TRUE" } */
where they emit UNKNOWN instead.

The root cause is that gimple has a byte-based twos-complement offset
of -16 expressed like this:
  _55 = q_92 + 4294967280;  (32-bit)
or:
  _55 = q_92 + 18446744073709551600; (64-bit)

Within region_model::convert_byte_offset_to_array_index that unsigned
offset was being divided by the element size to get an offset within
an array.

This happened to work on 64-bit target and host, but not elsewhere;
the offset needs to be converted to a signed type before the division
is meaningful.

This patch does so, fixing the failures.

gcc/analyzer/ChangeLog:
	PR analyzer/93281
	* region-model.cc
	(region_model::convert_byte_offset_to_array_index): Convert to
	ssizetype before dividing by byte_size.  Use fold_binary rather
	than fold_build2 to avoid needlessly constructing a tree for the
	non-const case.
This commit is contained in:
David Malcolm 2020-01-15 15:55:11 -05:00
parent e5e07b6818
commit 5f0303833d
2 changed files with 15 additions and 4 deletions
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9
gcc/analyzer/ChangeLog
View File

@ -1,3 +1,12 @@
2020-01-17 David Malcolm <dmalcolm@redhat.com>
PR analyzer/93281
* region-model.cc
(region_model::convert_byte_offset_to_array_index): Convert to
ssizetype before dividing by byte_size. Use fold_binary rather
than fold_build2 to avoid needlessly constructing a tree for the
non-const case.
2020-01-15 David Malcolm <dmalcolm@redhat.com>
* engine.cc (class impl_region_model_context): Fix comment.

10
gcc/analyzer/region-model.cc
View File

@ -6414,11 +6414,13 @@ region_model::convert_byte_offset_to_array_index (tree ptr_type,
/* This might not be a constant. */
tree byte_size = size_in_bytes (elem_type);
/* Try to get a constant by dividing, ensuring that we're in a
signed representation first. */
tree index
= fold_build2 (TRUNC_DIV_EXPR, integer_type_node,
offset_cst, byte_size);
if (CONSTANT_CLASS_P (index))
= fold_binary (TRUNC_DIV_EXPR, ssizetype,
fold_convert (ssizetype, offset_cst),
fold_convert (ssizetype, byte_size));
if (index && TREE_CODE (index) == INTEGER_CST)
return get_or_create_constant_svalue (index);
}