From e7c482b08076bb299742883c4ffd65b31e33200c Mon Sep 17 00:00:00 2001 From: Richard Biener Date: Wed, 25 May 2022 11:49:03 +0200 Subject: [PATCH] tree-optimization/105726 - adjust array bound heuristic There's heuristic to detect ptr[1].a[...] out of bound accesses reasoning that if ptr points to an array of aggregates a trailing incomplete array has to have size zero. The following more thoroughly constrains the cases this applies to avoid false positive diagnostics. 2022-05-25 Richard Biener PR tree-optimization/105726 * gimple-ssa-warn-restrict.cc (builtin_memref::set_base_and_offset): Constrain array-of-flexarray case more. * g++.dg/warn/Warray-bounds-27.C: New testcase. --- gcc/gimple-ssa-warn-restrict.cc | 20 ++++++++++++-------- gcc/testsuite/g++.dg/warn/Warray-bounds-27.C | 16 ++++++++++++++++ 2 files changed, 28 insertions(+), 8 deletions(-) create mode 100644 gcc/testsuite/g++.dg/warn/Warray-bounds-27.C diff --git a/gcc/gimple-ssa-warn-restrict.cc b/gcc/gimple-ssa-warn-restrict.cc index b678e806da3..734cdd7f5b4 100644 --- a/gcc/gimple-ssa-warn-restrict.cc +++ b/gcc/gimple-ssa-warn-restrict.cc @@ -525,7 +525,6 @@ builtin_memref::set_base_and_offset (tree expr) { tree memrefoff = fold_convert (ptrdiff_type_node, TREE_OPERAND (base, 1)); extend_offset_range (memrefoff); - base = TREE_OPERAND (base, 0); if (refoff != HOST_WIDE_INT_MIN && TREE_CODE (expr) == COMPONENT_REF) @@ -538,14 +537,19 @@ builtin_memref::set_base_and_offset (tree expr) REFOFF is set to s[1].b - (char*)s. */ offset_int off = tree_to_shwi (memrefoff); refoff += off; - } - if (!integer_zerop (memrefoff)) - /* A non-zero offset into an array of struct with flexible array - members implies that the array is empty because there is no - way to initialize such a member when it belongs to an array. - This must be some sort of a bug. */ - refsize = 0; + if (!integer_zerop (memrefoff) + && !COMPLETE_TYPE_P (TREE_TYPE (expr)) + && multiple_of_p (sizetype, memrefoff, + TYPE_SIZE_UNIT (TREE_TYPE (base)), true)) + /* A non-zero offset into an array of struct with flexible array + members implies that the array is empty because there is no + way to initialize such a member when it belongs to an array. + This must be some sort of a bug. */ + refsize = 0; + } + + base = TREE_OPERAND (base, 0); } if (TREE_CODE (ref) == COMPONENT_REF) diff --git a/gcc/testsuite/g++.dg/warn/Warray-bounds-27.C b/gcc/testsuite/g++.dg/warn/Warray-bounds-27.C new file mode 100644 index 00000000000..06ce089c4b0 --- /dev/null +++ b/gcc/testsuite/g++.dg/warn/Warray-bounds-27.C @@ -0,0 +1,16 @@ +// PR105726 +// { dg-do compile } +// { dg-require-effective-target c++11 } +// { dg-options "-O2 -Warray-bounds" } + +#include +#include + +struct X { + char pad[4]; + std::array mField; +}; + +void encode(char* aBuffer, const X& aMessage) { + strncpy(aBuffer, aMessage.mField.data(), 1); // { dg-bogus "bounds" } +}