We started to reject this testcase with r269078, whereby we perform constexpr evaluation on pre-cp_fold_function bodies. In this test that causes a problem because the offset argument of a PREINCREMENT_EXPR was a FLOAT_EXPR, and then the call to fold_build2 doesn't produce a REAL_CST and VERIFY_CONSTANT triggers.
So we need to fold the offset. But we can't use cxx_eval_constant_expression because offset can be stuff like "(int*) 4" which is invalid in constexpr. But we have fold_simple which uses const_unop, and that is precisely the function that can bash those FLOAT_EXPRs down to REAL_CSTs. Bootstrapped/regtested on x86_64-linux, ok for trunk/9? 2019-09-10 Marek Polacek <pola...@redhat.com> PR c++/91705 - constexpr evaluation rejects ++/-- on floats. * constexpr.c (cxx_eval_increment_expression): Call fold_simple on the offset. * g++.dg/cpp1y/constexpr-incr2.C: New test. diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c index 6c547d6d179..58db691e134 100644 --- gcc/cp/constexpr.c +++ gcc/cp/constexpr.c @@ -4164,6 +4164,10 @@ cxx_eval_increment_expression (const constexpr_ctx *ctx, tree t, tree offset = TREE_OPERAND (t, 1); gcc_assert (TREE_CONSTANT (offset)); + /* OFFSET is constant, but perhaps not constant enough. We need to + e.g. bash FLOAT_EXPRs to REAL_CSTs. */ + offset = fold_simple (offset); + /* The operand as an lvalue. */ op = cxx_eval_constant_expression (ctx, op, true, non_constant_p, overflow_p); diff --git gcc/testsuite/g++.dg/cpp1y/constexpr-incr2.C gcc/testsuite/g++.dg/cpp1y/constexpr-incr2.C new file mode 100644 index 00000000000..0d22851e4b2 --- /dev/null +++ gcc/testsuite/g++.dg/cpp1y/constexpr-incr2.C @@ -0,0 +1,66 @@ +// PR c++/91705 - constexpr evaluation rejects ++/-- on floats. +// { dg-do compile { target c++14 } } + +#define SA(X) static_assert((X),#X) + +template <class T> +constexpr T fn1(T t) +{ + return ++t; +} + +constexpr float fn2(float t) +{ + return ++t; +} + +template <class T> +constexpr T fn3(T t) +{ + return --t; +} + +constexpr float fn4(float t) +{ + return --t; +} + +template <class T> +constexpr T fn5(T t) +{ + return t++; +} + +constexpr float fn6(float t) +{ + return t++; +} + +template <class T> +constexpr T fn7(T t) +{ + return t--; +} + +constexpr float fn8(float t) +{ + return t--; +} + +constexpr double r1 = fn1(2.0f); +SA(r1 == 3); +constexpr double r2 = fn2(2.0f); +SA(r2 == 3); +constexpr double r3 = fn3(2.0f); +SA(r3 == 1); +constexpr double r4 = fn4(2.0f); +SA(r4 == 1); + +constexpr double r5 = fn5(2.0f); +SA(r5 == 2); +constexpr double r6 = fn6(2.0f); +SA(r6 == 2); +constexpr double r7 = fn7(2.0f); +SA(r7 == 2); +constexpr double r8 = fn8(2.0f); +SA(r8 == 2);