On 3/25/22 12:07, Patrick Palka wrote:
When an if-stmt is deemed non-constant because both of its branches are non-constant, we issue a rather generic error which, given that it points to the 'if' token, misleadingly suggests the condition is at fault:constexpr-105050.C:8:3: error: expression ‘<statement>’ is not a constant expression 8 | if (p != q && *p < 0) | ^~ This patch clarifies the error message to read: constexpr-105050.C:8:3: error: neither branch of ‘if’ is a constant expression 8 | if (p != q && *p < 0) | ^~ Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk?
OK. I wonder if we want to then diagnose the branches individually, but let's leave that for stage 1, if at all.
PR c++/105050 gcc/cp/ChangeLog: * constexpr.cc (potential_constant_expression_1) <case IF_STMT>: Clarify error message when a if-stmt is non-constant because its branches are non-constant. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/constexpr-105050.C: New test. --- gcc/cp/constexpr.cc | 7 ++++++- gcc/testsuite/g++.dg/cpp1y/constexpr-105050.C | 12 ++++++++++++ 2 files changed, 18 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-105050.C diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index 778680b8270..9c40b051574 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -9439,7 +9439,12 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now, } } if (flags & tf_error) - error_at (loc, "expression %qE is not a constant expression", t); + { + if (TREE_CODE (t) == IF_STMT) + error_at (loc, "neither branch of %<if%> is a constant expression"); + else + error_at (loc, "expression %qE is not a constant expression", t); + } return false;case VEC_INIT_EXPR:diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-105050.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-105050.C new file mode 100644 index 00000000000..99d5c9960ac --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-105050.C @@ -0,0 +1,12 @@ +// PR c++/105050 +// { dg-do compile { target c++14 } } + +void g(); +void h(); + +constexpr void f(int* p, int *q) { + if (p != q && *p < 0) // { dg-error "neither branch of 'if' is a constant expression" } + g(); + else + h(); +}
