Here, the problem was that the constexpr code for handling assignments within a constexpr function, or to a temporary object created within the constant-expression, was also allowing assignment to the target of the initialization. Fixed by specifically excluding that case.
Tested x86_64-pc-linux-gnu, applying to trunk.
commit 13c6ee3097eb21b4e1594504fda53c479b194796 Author: Jason Merrill <ja...@redhat.com> Date: Wed Feb 15 16:55:39 2017 -0500 PR c++/78572 - ICE with self-modifying array initializer * constexpr.c (cxx_eval_store_expression): The object we're initializing is outside the constant-expression. diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index 004bb45..fc7d46c 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -1635,6 +1635,7 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t, constexpr_ctx ctx_with_save_exprs = *ctx; hash_set<tree> save_exprs; ctx_with_save_exprs.save_exprs = &save_exprs; + ctx_with_save_exprs.call = &new_call; tree jump_target = NULL_TREE; cxx_eval_constant_expression (&ctx_with_save_exprs, body, @@ -3386,7 +3387,13 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t, /* And then find/build up our initializer for the path to the subobject we're initializing. */ tree *valp; - if (DECL_P (object)) + if (object == ctx->object && VAR_P (object) + && DECL_NAME (object) && ctx->call == NULL) + /* The variable we're building up an aggregate initializer for is outside + the constant-expression, so don't evaluate the store. We check + DECL_NAME to handle TARGET_EXPR temporaries, which are fair game. */ + valp = NULL; + else if (DECL_P (object)) valp = ctx->values->get (object); else valp = NULL; diff --git a/gcc/testsuite/g++.dg/init/array47.C b/gcc/testsuite/g++.dg/init/array47.C new file mode 100644 index 0000000..e3cb1b8 --- /dev/null +++ b/gcc/testsuite/g++.dg/init/array47.C @@ -0,0 +1,3 @@ +// PR c++/78572 + +static int array[10] = { array[3]=5, array[7]=3, };