tms34010: accept the optimizer's returned argument attribute

llvm/lib/Target/TMS34010/TMS34010ISelLowering.cpp

@@ -70,11 +70,15 @@ SDValue TMS34010TargetLowering::LowerFormalArguments(
   // elimination).
   for (unsigned i = 0, e = Ins.size(); i != e; ++i) {
     const ISD::InputArg &In = Ins[i];
+    // `returned` is an optimization hint, not an ABI feature: the argument is
+    // still passed in its normal stack slot, and the callee already returns
+    // through the ABI's A8.  The optimizer infers it for ordinary C such as
+    // `int first(int a, int b) { return a; }`, so rejecting it made valid -O2
+    // input uncompilable.  The ABI-affecting flags stay rejected.
     if (In.Flags.isSRet() || In.Flags.isByVal() || In.Flags.isInReg() ||
-        In.Flags.isNest() || In.Flags.isReturned())
+        In.Flags.isNest())
       report_fatal_error(
-          "M2 supports only plain arguments "
-          "(no sret/byval/inreg/nest/returned)",
+          "M2 supports only plain arguments (no sret/byval/inreg/nest)",
           false);
     if (In.VT != MVT::i32)
       report_fatal_error("M2 supports only i32 and pointer arguments", false);

llvm/test/CodeGen/TMS34010/m2-reject-sret.ll

@@ -3,7 +3,7 @@
 ;
 ; M2 has no sret convention.  The pointer attribute must be rejected even
 ; though its legalized type is a plain i32.
-; CHECK: M2 supports only plain arguments (no sret/byval/inreg/nest/returned)
+; CHECK: M2 supports only plain arguments (no sret/byval/inreg/nest)
 define void @sret_arg(ptr sret(i32) %out) {
 entry:
   store i32 0, ptr %out

llvm/test/CodeGen/TMS34010/m2-returned.ll

@@ -0,0 +1,15 @@
+; RUN: llc -march=tms34010 -O0 -filetype=asm < %s | FileCheck %s
+; RUN: llc -march=tms34010 -O2 -filetype=asm < %s | FileCheck %s
+;
+; `returned` is an optimizer hint, not an ABI convention: the optimizer infers
+; it for `return a`, and the argument still lives in its normal FP-relative
+; stack slot.  It must not be rejected.
+define i32 @first(i32 returned %a, i32 %b) {
+entry:
+  ret i32 %a
+}
+; CHECK-LABEL: _first:
+; CHECK: MOVE A13, -*SP, 1
+; CHECK: ADDI -32, A{{[0-9]+}}
+; CHECK: MOVE {{A[0-9]+}}, A8
+; CHECK: RETS 2