[gcc r15-7731] c++: ICE with GOTO_EXPR [PR118928]

[Marek Polacek via Gcc-cvs]

https://gcc.gnu.org/g:9792126ac769f2962c0f305991818c64f9e51221

commit r15-7731-g9792126ac769f2962c0f305991818c64f9e51221
Author: Marek Polacek <pola...@redhat.com>
Date:   Wed Feb 19 14:06:33 2025 -0500

    c++: ICE with GOTO_EXPR [PR118928]
    
    In this PR we crash in cxx_eval_constant_expression/GOTO_EXPR on:
    
      gcc_assert (cxx_dialect >= cxx23);
    
    The code obviously doesn't expect to see a goto pre-C++23.  But we can
    get here with the new prvalue optimization.  In this test we found
    ourselves in synthesize_method for X::X().  This function calls:
    
     a) finish_function, which does cp_genericize -> ... -> genericize_c_loops,
        which creates the GOTO_EXPR;
     b) expand_or_defer_fn -> maybe_clone_body -> ... -> cp_fold_function
        where we reach the new maybe_constant_init call and crash on the
        goto.
    
    Since we can validly get to that assert, I think we should just remove
    it.  I don't see other similar asserts like this one.
    
            PR c++/118928
    
    gcc/cp/ChangeLog:
    
            * constexpr.cc (cxx_eval_constant_expression) <case GOTO_EXPR>: 
Remove
            an assert.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/constexpr-prvalue5.C: New test.
    
    Reviewed-by: Jason Merrill <ja...@redhat.com>

Diff:
---
 gcc/cp/constexpr.cc                             |  1 -
 gcc/testsuite/g++.dg/cpp0x/constexpr-prvalue5.C | 24 ++++++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 59dd0668af3f..c68666cc5ddc 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -8691,7 +8691,6 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, 
tree t,
        *jump_target = TREE_OPERAND (t, 0);
       else
        {
-         gcc_assert (cxx_dialect >= cxx23);
          if (!ctx->quiet)
            error_at (loc, "%<goto%> is not a constant expression");
          *non_constant_p = true;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-prvalue5.C 
b/gcc/testsuite/g++.dg/cpp0x/constexpr-prvalue5.C
new file mode 100644
index 000000000000..1f847bbe183e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-prvalue5.C
@@ -0,0 +1,24 @@
+// PR c++/118928
+// { dg-do compile { target c++11 } }
+// { dg-options "-O" }
+
+using size_t = decltype(sizeof(0));
+
+namespace std {
+template <typename T> struct initializer_list {
+  const T *_M_array;
+  size_t _M_len;
+};
+struct S {
+  constexpr S(const char *); // { dg-warning "used but never defined" }
+};
+struct vector {
+  constexpr vector(initializer_list<S>) {}
+};
+}
+struct Y {
+    std::vector v;
+};
+struct X {
+  Y y{{""}};
+} x;