On Tue, Sep 10, 2024 at 10:37:31AM -0400, Jason Merrill wrote: > On 8/29/24 12:23 PM, Marek Polacek wrote: > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/14? > > > > -- >8 -- > > Pre r14-4793, we'd call warn_tautological_cmp -> operand_equal_p > > with operands wrapped in NON_DEPENDENT_EXPR, which works, since > > o_e_p bails for codes it doesn't know. But now we pass operands > > not encapsulated in NON_DEPENDENT_EXPR, and crash, because the > > template tree for &a[x] has null DECL_FIELD_OFFSET. > > Why are we trying to compare DECL_FIELD_OFFSET in C++, anyway? I'd think we > should limit that to C and in C++ rely on FIELD_DECL identity.
This goes back to r12-7797. I suppose it's trying to handle C++ because we can't use c_dialect_cxx () in fold-const. I know there's lang_GNU_CXX but I suggest we do the following. > > I don't think I meant this warning to be called in a template, > > so let's avoid the problem this easy way. > > Hmm, it seems potentially useful in a template, especially since we suppress > it in instantiations. Ack. How about this? Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? -- >8 -- Pre r14-4793, we'd call warn_tautological_cmp -> operand_equal_p with operands wrapped in NON_DEPENDENT_EXPR, which works, since o_e_p bails for codes it doesn't know. But now we pass operands not encapsulated in NON_DEPENDENT_EXPR, and crash, because the template tree for &a[x] has null DECL_FIELD_OFFSET. This patch extends r12-7797 to cover the case when DECL_FIELD_OFFSET is null. PR c++/116534 gcc/ChangeLog: * fold-const.cc (operand_compare::operand_equal_p): Check DECL_FIELD_OFFSET. gcc/testsuite/ChangeLog: * g++.dg/warn/Wtautological-compare4.C: New test. --- gcc/fold-const.cc | 16 ++++++++------ .../g++.dg/warn/Wtautological-compare4.C | 21 +++++++++++++++++++ 2 files changed, 31 insertions(+), 6 deletions(-) create mode 100644 gcc/testsuite/g++.dg/warn/Wtautological-compare4.C diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc index 70db16759d0..3da09621584 100644 --- a/gcc/fold-const.cc +++ b/gcc/fold-const.cc @@ -3601,12 +3601,16 @@ operand_compare::operand_equal_p (const_tree arg0, const_tree arg1, /* Non-FIELD_DECL operands can appear in C++ templates. */ if (TREE_CODE (field0) != FIELD_DECL - || TREE_CODE (field1) != FIELD_DECL - || !operand_equal_p (DECL_FIELD_OFFSET (field0), - DECL_FIELD_OFFSET (field1), flags) - || !operand_equal_p (DECL_FIELD_BIT_OFFSET (field0), - DECL_FIELD_BIT_OFFSET (field1), - flags)) + || TREE_CODE (field1) != FIELD_DECL) + return false; + + if (DECL_FIELD_OFFSET (field0) + && DECL_FIELD_OFFSET (field1) + && (!operand_equal_p (DECL_FIELD_OFFSET (field0), + DECL_FIELD_OFFSET (field1), flags) + || !operand_equal_p (DECL_FIELD_BIT_OFFSET (field0), + DECL_FIELD_BIT_OFFSET (field1), + flags))) return false; } else diff --git a/gcc/testsuite/g++.dg/warn/Wtautological-compare4.C b/gcc/testsuite/g++.dg/warn/Wtautological-compare4.C new file mode 100644 index 00000000000..96308f49a42 --- /dev/null +++ b/gcc/testsuite/g++.dg/warn/Wtautological-compare4.C @@ -0,0 +1,21 @@ +// PR c++/116534 +// { dg-do compile } +// { dg-options "-Wall" } + +template <class A> +struct Test { + bool foo(unsigned x, unsigned y) { + bool test = &a[x] == &b[y]; + return test; + } + unsigned *a; + unsigned *b; +}; + +void +g () +{ + Test<int> t; + t.foo (0u, 1u); + t.foo (0u, 0u); +} base-commit: f5448384a2134f32c8733b401440da11bfe69252 -- 2.46.0