[SelectionDAGBuilder] Make sure DemoteReg ends up in right reg-class.

The virtual register containing the address for returned value on
stack should in the DAG be represented with a CopyFromReg node and not
a Register node. Otherwise, InstrEmitter will not make sure that it
ends up in the right register class for the target instruction.

SystemZ needs this, becuause the reg class for address registers is a
subset of the general 64 bit register class.

test/SystemZ/CodeGen/args-07.ll and args-04.ll updated to run with
-verify-machineinstrs.

Reviewed by Hal Finkel.

llvm-svn: 253461

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -1344,7 +1344,8 @@ void SelectionDAGBuilder::visitRet(const ReturnInst &I) {
     ComputeValueVTs(TLI, DL, PointerType::getUnqual(F->getReturnType()),
                     PtrValueVTs);
 
-    SDValue RetPtr = DAG.getRegister(DemoteReg, PtrValueVTs[0]);
+    SDValue RetPtr = DAG.getCopyFromReg(DAG.getEntryNode(), getCurSDLoc(),
+                                        DemoteReg, PtrValueVTs[0]);
     SDValue RetOp = getValue(I.getOperand(0));
 
     SmallVector<EVT, 4> ValueVTs;

test/CodeGen/SystemZ/args-04.ll

@@ -1,7 +1,7 @@
 ; Test incoming GPR, FPR and stack arguments when no extension type is given.
 ; This type of argument is used for passing structures, etc.
 ;
-; RUN: llc < %s -mtriple=s390x-linux-gnu | FileCheck %s
+; RUN: llc < %s -mtriple=s390x-linux-gnu -verify-machineinstrs | FileCheck %s
 
 ; Do some arithmetic so that we can see the register being used.
 define i8 @f1(i8 %r2) {

test/CodeGen/SystemZ/args-07.ll

@@ -1,6 +1,6 @@
 ; Test multiple return values (LLVM ABI extension)
 ;
-; RUN: llc < %s -mtriple=s390x-linux-gnu | FileCheck %s
+; RUN: llc < %s -mtriple=s390x-linux-gnu -verify-machineinstrs| FileCheck %s
 
 ; Up to four integer return values fit into GPRs.
 define { i64, i64, i64, i64 } @f1() {