[SystemZ] Define the return instruction as a pseudo alias of BR

This is the first of a few patches to reduce the dupliation of encoding
information.  The return instruction is a normal BR in which one of the
registers is fixed.

llvm-svn: 191364

3 files changed, 23 insertions, 8 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZAsmPrinter.cpp b/llvm/lib/Target/SystemZ/SystemZAsmPrinter.cpp
index 3a57ea0afd4..84227614c09 100644
--- a/llvm/lib/Target/SystemZ/SystemZAsmPrinter.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZAsmPrinter.cpp
@@ -19,6 +19,7 @@
 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
 #include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCInstBuilder.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Target/Mangler.h"
@@ -26,9 +27,16 @@
 using namespace llvm;
 
 void SystemZAsmPrinter::EmitInstruction(const MachineInstr *MI) {
-  SystemZMCInstLower Lower(Mang, MF->getContext(), *this);
   MCInst LoweredMI;
-  Lower.lower(MI, LoweredMI);
+  switch (MI->getOpcode()) {
+  case SystemZ::Return:
+    LoweredMI = MCInstBuilder(SystemZ::BR).addReg(SystemZ::R14D);
+    break;
+
+  default:
+    SystemZMCInstLower(Mang, MF->getContext(), *this).lower(MI, LoweredMI);
+    break;
+  }
   OutStreamer.EmitInstruction(LoweredMI);
 }
 
diff --git a/llvm/lib/Target/SystemZ/SystemZInstrFormats.td b/llvm/lib/Target/SystemZ/SystemZInstrFormats.td
index 7f2f9f8805d..b594f0e771f 100644
--- a/llvm/lib/Target/SystemZ/SystemZInstrFormats.td
+++ b/llvm/lib/Target/SystemZ/SystemZInstrFormats.td
@@ -1467,3 +1467,13 @@ multiclass StringRRE<string mnemonic, bits<16> opcode,
                       [(set GR64:$end, (operator GR64:$start1, GR64:$start2,
                                                  GR32:$char))]>;
 }
+
+// A pseudo instruction that is a direct alias of a real instruction.
+// These aliases are used in cases where a particular register operand is
+// fixed or where the same instruction is used with different register sizes.
+// The size parameter is the size in bytes of the associated real instruction.
+class Alias<int size, dag outs, dag ins, list<dag> pattern>
+  : InstSystemZ<size, outs, ins, "", pattern> {
+  let isPseudo = 1;
+  let isCodeGenOnly = 1;
+}
diff --git a/llvm/lib/Target/SystemZ/SystemZInstrInfo.td b/llvm/lib/Target/SystemZ/SystemZInstrInfo.td
index ca678ab7559..94701726d50 100644
--- a/llvm/lib/Target/SystemZ/SystemZInstrInfo.td
+++ b/llvm/lib/Target/SystemZ/SystemZInstrInfo.td
@@ -32,12 +32,9 @@ let neverHasSideEffects = 1 in {
 // Control flow instructions
 //===----------------------------------------------------------------------===//
 
-// A return instruction.  R1 is the condition-code mask (all 1s)
-// and R2 is the target address, which is always stored in %r14.
-let isReturn = 1, isTerminator = 1, isBarrier = 1, hasCtrlDep = 1,
-    R1 = 15, R2 = 14, isCodeGenOnly = 1 in {
-  def RET : InstRR<0x07, (outs), (ins), "br\t%r14", [(z_retflag)]>;
-}
+// A return instruction (br %r14).
+let isReturn = 1, isTerminator = 1, isBarrier = 1, hasCtrlDep = 1 in
+  def Return : Alias<2, (outs), (ins), [(z_retflag)]>;
 
 // Unconditional branches.  R1 is the condition-code mask (all 1s).
 let isBranch = 1, isTerminator = 1, isBarrier = 1, R1 = 15 in {