Emit an error message on unsupported llvm_asm

llvm_asm was never meant to be completely supported since it has been
replaced with the asm macro but we still need it to compile some parts
of libcore, previously the compiler was aborting when an unsupported
llvm_asm construct was found.

gcc/rust/ChangeLog:

	* ast/rust-expr.h: Add const getters to llvm members.
	* hir/rust-ast-lower-expr.cc (check_llvm_asm_support): Check llvm_asm
	usage validity.
	(ASTLoweringExpr::visit): Emit an error message instead of aborting.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

Author: P-E-P

gcc/rust/ast/rust-expr.h

@@ -5669,6 +5669,10 @@ class LlvmInlineAsm : public ExprWithoutBlock
   }
 
   std::vector<TupleTemplateStr> &get_templates () { return templates; }
+  const std::vector<TupleTemplateStr> &get_templates () const
+  {
+    return templates;
+  }
 
   Expr::Kind get_expr_kind () const override
   {
@@ -5687,9 +5691,12 @@ class LlvmInlineAsm : public ExprWithoutBlock
   void set_outputs (std::vector<LlvmOperand> operands) { outputs = operands; }
 
   std::vector<LlvmOperand> &get_inputs () { return inputs; }
+  const std::vector<LlvmOperand> &get_inputs () const { return inputs; }
   std::vector<LlvmOperand> &get_outputs () { return outputs; }
+  const std::vector<LlvmOperand> &get_outputs () const { return outputs; }
 
   std::vector<TupleClobber> &get_clobbers () { return clobbers; }
+  const std::vector<TupleClobber> &get_clobbers () const { return clobbers; }
 };
 
 } // namespace AST

gcc/rust/hir/rust-ast-lower-expr.cc

@@ -994,6 +994,23 @@ ASTLoweringExpr::visit (AST::InlineAsm &expr)
 			  expr.get_options (), mapping);
 }
 
+namespace {
+// We're not really supporting llvm_asm, only the bare minimum for libcore's
+// blackbox
+// llvm_asm!("" : : "r"(&mut dummy) : "memory" : "volatile");
+bool
+check_llvm_asm_support (const std::vector<LlvmOperand> &inputs,
+			const std::vector<LlvmOperand> &outputs,
+			const AST::LlvmInlineAsm &expr)
+{
+  return outputs.size () == 0 && inputs.size () <= 1
+	 && expr.get_clobbers ().size () <= 1
+	 && expr.get_templates ().size () == 1
+	 && expr.get_templates ()[0].symbol == "";
+}
+
+} // namespace
+
 void
 ASTLoweringExpr::visit (AST::LlvmInlineAsm &expr)
 {
@@ -1026,13 +1043,15 @@ ASTLoweringExpr::visit (AST::LlvmInlineAsm &expr)
 				      expr.is_stack_aligned (),
 				      expr.get_dialect ()};
 
-  // We're not really supporting llvm_asm, only the bare minimum
-  // we're quite conservative here as the current code support more usecase.
-  rust_assert (outputs.size () == 0);
-  rust_assert (inputs.size () <= 1);
-  rust_assert (expr.get_clobbers ().size () <= 1);
-  rust_assert (expr.get_templates ().size () == 1);
-  rust_assert (expr.get_templates ()[0].symbol == "");
+  if (!check_llvm_asm_support (inputs, outputs, expr))
+    {
+      rust_error_at (expr.get_locus (), "unsupported %qs construct",
+		     "llvm_asm");
+      rust_inform (
+	expr.get_locus (),
+	"%<llvm_asm%> has been replaced with %<asm%>, gccrs only supports a "
+	"subset of %<llvm_asm%> to compile libcore");
+    }
 
   translated
     = new HIR::LlvmInlineAsm (expr.get_locus (), inputs, outputs,