| Message ID | ZuhmIGkKerQjKj5I@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] c++: ICE with -Wtautological-compare in template [PR116534] | expand |
On 9/16/24 7:08 PM, Marek Polacek wrote: > 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))) If at least one has null FIELD_OFFSET, I'd think we still want to compare them for being ==, this seems to assume that a field with null offset is equal to any other field. > 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
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); +}