mirror of git://gcc.gnu.org/git/gcc.git
c++: prvalue array decay [PR94264]
My change for PR53220 made array to pointer decay for prvalue arrays ill-formed to catch well-defined C code that produces a dangling pointer in C++ due to the shorter lifetime of compound literals. This wasn't really correct, but wasn't a problem until C++17 added prvalue arrays, at which point it started rejecting valid C++ code. I wanted to make sure that we still diagnose the problematic code; -Wdangling-pointer covers the array-lit.c case, but I needed to extend -Wreturn-local-addr to handle the return case. PR c++/94264 PR c++/53220 gcc/c/ChangeLog: * c-typeck.cc (array_to_pointer_conversion): Adjust -Wc++-compat diagnostic. gcc/cp/ChangeLog: * call.cc (convert_like_internal): Remove obsolete comment. * typeck.cc (decay_conversion): Allow array prvalue. (maybe_warn_about_returning_address_of_local): Check for returning pointer to temporary. gcc/testsuite/ChangeLog: * c-c++-common/array-lit.c: Adjust. * g++.dg/cpp1z/array-prvalue1.C: New test. * g++.dg/ext/complit17.C: New test.
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@ -1748,7 +1748,7 @@ array_to_pointer_conversion (location_t loc, tree exp)
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if (!TREE_READONLY (decl) && !TREE_STATIC (decl))
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warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wc___compat,
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"converting an array compound literal to a pointer "
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"is ill-formed in C++");
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"leads to a dangling pointer in C++");
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}
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adr = build_unary_op (loc, ADDR_EXPR, exp, true);
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@ -8578,8 +8578,6 @@ convert_like_internal (conversion *convs, tree expr, tree fn, int argnum,
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array = finish_compound_literal (array, new_ctor, complain);
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/* This is dubious now, should be blessed by P2752. */
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DECL_MERGEABLE (TARGET_EXPR_SLOT (array)) = true;
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/* Take the address explicitly rather than via decay_conversion
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to avoid the error about taking the address of a temporary. */
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array = cp_build_addr_expr (array, complain);
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}
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else
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@ -2534,15 +2534,6 @@ decay_conversion (tree exp,
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return error_mark_node;
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}
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/* Don't let an array compound literal decay to a pointer. It can
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still be used to initialize an array or bind to a reference. */
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if (TREE_CODE (exp) == TARGET_EXPR)
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{
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if (complain & tf_error)
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error_at (loc, "taking address of temporary array");
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return error_mark_node;
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}
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ptrtype = build_pointer_type (TREE_TYPE (type));
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if (VAR_P (exp))
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@ -10535,6 +10526,9 @@ maybe_warn_about_returning_address_of_local (tree retval, location_t loc)
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if (TYPE_REF_P (valtype))
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warning_at (loc, OPT_Wreturn_local_addr,
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"returning reference to temporary");
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else if (TYPE_PTR_P (valtype))
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warning_at (loc, OPT_Wreturn_local_addr,
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"returning pointer to temporary");
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else if (is_std_init_list (valtype))
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warning_at (loc, OPT_Winit_list_lifetime,
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"returning temporary %<initializer_list%> does not extend "
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@ -1,10 +1,11 @@
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/* { dg-options "-std=c99 -Wc++-compat -Werror" { target c } } */
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/* { dg-options "-Werror=dangling-pointer=1" { target c++ } } */
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/* { dg-prune-output "treated as errors" } */
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#include <stdio.h>
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int main()
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{
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for (int *p = (int[]){ 1, 2, 3, 0 }; /* { dg-error "array" } */
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for (int *p = (int[]){ 1, 2, 3, 0 }; /* { dg-error "array|temporary" } */
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*p; ++p) {
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printf("%d\n", *p);
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}
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@ -0,0 +1,7 @@
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// PR c++/94264
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// { dg-do compile { target c++17 } }
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int main() {
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using T = int[];
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T{1, 2} == nullptr;
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}
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@ -0,0 +1,4 @@
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// PR c++/53220
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// { dg-options "" }
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int* f() { return (int[]){42}; } // { dg-warning "pointer to temporary" }
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