c++: constexpr folding in unevaluated context [PR105931]
Changing the type of N from int to unsigned in decltype82.C (from
r13-986-g0ecb6b906f215e) reveals another spot where we perform constexpr
evaluation in an unevaluated context for sake of warnings, this time
from the call to shorten_compare in cp_build_binary_op, which calls
fold_for_warn.
We could (and probably should) suppress the shorten_compare warnings
when in an unevaluated context, but there's probably other callers of
fold_for_warn that are similarly affected. So this patch takes the
approach of directly suppressing fold_for_warn when in an unevaluated
context.
PR c++/105931
gcc/cp/ChangeLog:
* expr.cc (fold_for_warn): Don't fold when in an unevaluated
context.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/decltype82a.C: New test.
(cherry picked from commit b00b95198e
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@ -397,6 +397,11 @@ fold_for_warn (tree x)
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{
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/* C++ implementation. */
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if (cp_unevaluated_operand)
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/* In an unevaluated context we don't care about the reduced value
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of an expression, so neither should any warnings. */
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return x;
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/* Prevent warning-dependent constexpr evaluation from changing
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DECL_UID (which breaks -fcompare-debug) and from instantiating
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templates. */
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@ -0,0 +1,11 @@
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// PR c++/105931
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// { dg-do compile { target c++11 } }
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// A version of decltype82.C where N is unsigned.
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template<unsigned N>
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void f() {
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using ty1 = decltype((5 % N) == 0);
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using ty2 = decltype((5 / N) == 0);
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}
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template void f<0>();
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