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* [gcc/devel/gccgo] analyzer: fix handling of negative byte offsets (v2) (PR 93281)
@ 2020-01-23 0:27 Ian Lance Taylor
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From: Ian Lance Taylor @ 2020-01-23 0:27 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:5f0303833d542b273da33e4b149974e739d350e5
commit 5f0303833d542b273da33e4b149974e739d350e5
Author: David Malcolm <dmalcolm@redhat.com>
Date: Wed Jan 15 15:55:11 2020 -0500
analyzer: fix handling of negative byte offsets (v2) (PR 93281)
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.
Diff:
---
gcc/analyzer/ChangeLog | 9 +++++++++
gcc/analyzer/region-model.cc | 10 ++++++----
2 files changed, 15 insertions(+), 4 deletions(-)
diff --git a/gcc/analyzer/ChangeLog b/gcc/analyzer/ChangeLog
index 2ca7144..e809018 100644
--- a/gcc/analyzer/ChangeLog
+++ b/gcc/analyzer/ChangeLog
@@ -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.
diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index 5c39be4..f67572e 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -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);
}
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