On Wed, Aug 7, 2019, 2:35 PM Marek Polacek <pola...@redhat.com> wrote:
> On Wed, Aug 07, 2019 at 12:23:25PM -0400, Jason Merrill wrote: > > On Wed, Aug 7, 2019, 9:11 AM Marek Polacek <pola...@redhat.com> wrote: > > > > > On Tue, Aug 06, 2019 at 09:25:45PM -0400, Jason Merrill wrote: > > > > Let's downgrade the errors in earlier standard modes to pedwarn. Ok > with > > > > that change. > > > > > > Works for me, here's what I'll apply once it passes testing. > > > > > > I removed the diagnostic in potential_constant_expression_1/ASM_EXPR so > > > that > > > we don't generate duplicate pedwarns for the same thing. Hope that's > OK. > > > > > > 2019-08-07 Marek Polacek <pola...@redhat.com> > > > > > > PR c++/91346 - Implement P1668R1, allow unevaluated asm in > > > constexpr. > > > * constexpr.c (cxx_eval_constant_expression): Handle ASM_EXPR. > > > (potential_constant_expression_1) <case ASM_EXPR>: Allow. > > > * cp-tree.h (finish_asm_stmt): Adjust. > > > * parser.c (cp_parser_asm_definition): Grab the locaion of > "asm" > > > and > > > use it. Change an error to a pedwarn. Allow asm in C++2a, > warn > > > otherwise. > > > * pt.c (tsubst_expr): Pass a location down to finish_asm_stmt. > > > * semantics.c (finish_asm_stmt): New location_t parameter. > Use it. > > > > > > * g++.dg/cpp2a/inline-asm1.C: New test. > > > * g++.dg/cpp2a/inline-asm2.C: New test. > > > * g++.dg/cpp1y/constexpr-neg1.C: Adjust dg-error. > > > > > > diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c > > > index 36a66337433..e86b0789b84 100644 > > > --- gcc/cp/constexpr.c > > > +++ gcc/cp/constexpr.c > > > @@ -5289,6 +5289,18 @@ cxx_eval_constant_expression (const > constexpr_ctx > > > *ctx, tree t, > > > r = void_node; > > > break; > > > > > > + case ASM_EXPR: > > > + if (!ctx->quiet) > > > + { > > > + error_at (cp_expr_loc_or_input_loc (t), > > > + "inline assembly is not a constant expression"); > > > + inform (cp_expr_loc_or_input_loc (t), > > > + "only unevaluated inline assembly is allowed in a " > > > + "%<constexpr%> function in C++2a"); > > > + } > > > + *non_constant_p = true; > > > + return t; > > > + > > > default: > > > if (STATEMENT_CODE_P (TREE_CODE (t))) > > > { > > > @@ -6469,13 +6481,18 @@ potential_constant_expression_1 (tree t, bool > > > want_rval, bool strict, bool now, > > > /* GCC internal stuff. */ > > > case VA_ARG_EXPR: > > > case TRANSACTION_EXPR: > > > - case ASM_EXPR: > > > case AT_ENCODE_EXPR: > > > fail: > > > if (flags & tf_error) > > > error_at (loc, "expression %qE is not a constant expression", > t); > > > return false; > > > > > > + case ASM_EXPR: > > > + /* In C++2a, unevaluated inline assembly is permitted in > constexpr > > > + functions. If it's used in earlier standard modes, we > pedwarn in > > > + cp_parser_asm_definition. */ > > > + return true; > > > > > > > Actually, do we need this change? If it's (possibly) unevaluated, we > > shouldn't get here. > > We can get here when using asm() in ({ }) like this (ugh): > > constexpr int > foo (bool b) > { > if (b) > { > constexpr int i = ({ asm(""); 42; }); > return i; > } > else > return 42; > } > static_assert(foo(false) == 42, ""); > > With the current state of potential_constant_expression_1, we generate > > inline-asm3.C: In function ‘constexpr int foo(bool)’: > inline-asm3.C:10:27: error: inline assembly is not a constant expression > 10 | constexpr int i = ({ asm(""); 42; }); > | ^~~ > inline-asm3.C:10:27: note: only unevaluated inline assembly is allowed in > a ‘constexpr’ function in C++2a > > which I thought was better than what we emit with the hunk revered: > > inline-asm3.C: In function ‘constexpr int foo(bool)’: > inline-asm3.C:10:27: error: expression ‘<statement>’ is not a constant > expression > 10 | constexpr int i = ({ asm(""); 42; }); > | ^~~ > > But I'm happy to revert that hunk if you want. > Sure, perhaps we could share the error message between the two functions. In general it's better to reject something in potential_... if we can. >