From 5f0303833d542b273da33e4b149974e739d350e5 Mon Sep 17 00:00:00 2001 From: David Malcolm Date: Wed, 15 Jan 2020 15:55:11 -0500 Subject: [PATCH] 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. --- 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 2ca71441199..e8090184216 100644 --- a/gcc/analyzer/ChangeLog +++ b/gcc/analyzer/ChangeLog @@ -1,3 +1,12 @@ +2020-01-17 David Malcolm + + 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 * engine.cc (class impl_region_model_context): Fix comment. diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc index 5c39be4fd7f..f67572e2d45 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); } -- 2.30.2