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| author | Jakub Jelinek <jakub@redhat.com> | 2021-07-15 18:53:20 +0200 |
|---|---|---|
| committer | Jakub Jelinek <jakub@redhat.com> | 2021-07-15 18:53:20 +0200 |
| commit | 7094a69bd62a14dfa311eaa2fea468f221c7c9f3 (patch) | |
| tree | e035f180ebf7d79e731b6efed4f7e0efebd37a4d | |
| parent | b25edf6e6feeadc6a5aa337b8c725786227162dd (diff) | |
| download | gcc-7094a69bd62a14dfa311eaa2fea468f221c7c9f3.zip gcc-7094a69bd62a14dfa311eaa2fea468f221c7c9f3.tar.gz gcc-7094a69bd62a14dfa311eaa2fea468f221c7c9f3.tar.bz2 | |
c++: Optimize away NULLPTR_TYPE comparisons [PR101443]
Comparisons of NULLPTR_TYPE operands cause all kinds of problems in the
middle-end and in fold-const.c, various optimizations assume that if they
see e.g. a non-equality comparison with one of the operands being
INTEGER_CST and it is not INTEGRAL_TYPE_P (which has TYPE_{MIN,MAX}_VALUE),
they can build_int_cst (type, 1) to find a successor.
The following patch fixes it by making sure they don't appear in the IL,
optimize them away at cp_fold time as all can be folded.
Though, I've just noticed that clang++ rejects the non-equality comparisons
instead, foo () > 0 with
invalid operands to binary expression ('decltype(nullptr)' (aka 'nullptr_t') and 'int')
and foo () > nullptr with
invalid operands to binary expression ('decltype(nullptr)' (aka 'nullptr_t') and 'nullptr_t')
Shall we reject those too, in addition or instead of parts of this patch?
If so, wouldn't this patch be still useful for backports, I bet we don't
want to start reject it on the release branches when we used to accept it.
2021-07-15 Jakub Jelinek <jakub@redhat.com>
PR c++/101443
* cp-gimplify.c (cp_fold): For comparisons with NULLPTR_TYPE
operands, fold them right away to true or false.
* g++.dg/cpp0x/nullptr46.C: New test.
| -rw-r--r-- | gcc/cp/cp-gimplify.c | 26 | ||||
| -rw-r--r-- | gcc/testsuite/g++.dg/cpp0x/nullptr46.C | 11 |
2 files changed, 37 insertions, 0 deletions
diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c index de37f2c..ff0bff7 100644 --- a/gcc/cp/cp-gimplify.c +++ b/gcc/cp/cp-gimplify.c @@ -2423,6 +2423,32 @@ cp_fold (tree x) op0 = cp_fold_maybe_rvalue (TREE_OPERAND (x, 0), rval_ops); op1 = cp_fold_rvalue (TREE_OPERAND (x, 1)); + /* decltype(nullptr) has only one value, so optimize away all comparisons + with that type right away, keeping them in the IL causes troubles for + various optimizations. */ + if (COMPARISON_CLASS_P (org_x) + && TREE_CODE (TREE_TYPE (op0)) == NULLPTR_TYPE + && TREE_CODE (TREE_TYPE (op1)) == NULLPTR_TYPE) + { + switch (code) + { + case EQ_EXPR: + case LE_EXPR: + case GE_EXPR: + x = constant_boolean_node (true, TREE_TYPE (x)); + break; + case NE_EXPR: + case LT_EXPR: + case GT_EXPR: + x = constant_boolean_node (false, TREE_TYPE (x)); + break; + default: + gcc_unreachable (); + } + return omit_two_operands_loc (loc, TREE_TYPE (x), x, + op0, op1); + } + if (op0 != TREE_OPERAND (x, 0) || op1 != TREE_OPERAND (x, 1)) { if (op0 == error_mark_node || op1 == error_mark_node) diff --git a/gcc/testsuite/g++.dg/cpp0x/nullptr46.C b/gcc/testsuite/g++.dg/cpp0x/nullptr46.C new file mode 100644 index 0000000..1514cee --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/nullptr46.C @@ -0,0 +1,11 @@ +// PR c++/101443 +// { dg-do compile { target c++11 } } +// { dg-options "-O2" } + +decltype(nullptr) foo (); + +bool +bar () +{ + return foo () > nullptr || foo () < nullptr; +} |