[SystemZ] Implement .machine (push|pop) directives

The `.machine push` and `.machine pop` directives were missing from
the SystemZ Backend Asm Parser. This commit adds them, and expands the
corresponding test to test proper operation.

Author: dominik-steenken

llvm/lib/Target/SystemZ/AsmParser/SystemZAsmParser.cpp

@@ -33,6 +33,7 @@
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/SMLoc.h"
+#include "llvm/TargetParser/SubtargetFeature.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
@@ -410,6 +411,18 @@ class SystemZAsmParser : public MCTargetAsmParser {
 
 private:
   MCAsmParser &Parser;
+
+  // A vector to contain the stack of FeatureBitsets created by `.machine push`.
+  // `.machine pop` pops the top of the stack and resets `CurrentFeatures` to
+  // the result.
+  SmallVector<FeatureBitset> MachineStack;
+  // Specifies the current FeatureBitset. It is initialized from the
+  // SubtargetInfo handed to the constructor of the AsmParser. During parsing,
+  // it always reflects the current FeatureBitset used to determine which
+  // machine features are available, i.e. either the default or the result
+  // of the most reecent `.machine` directive.
+  FeatureBitset CurrentFeatures;
+
   enum RegisterGroup {
     RegGR,
     RegFP,
@@ -494,16 +507,16 @@ class SystemZAsmParser : public MCTargetAsmParser {
 
 public:
   SystemZAsmParser(const MCSubtargetInfo &sti, MCAsmParser &parser,
-                   const MCInstrInfo &MII,
-                   const MCTargetOptions &Options)
-    : MCTargetAsmParser(Options, sti, MII), Parser(parser) {
+                   const MCInstrInfo &MII, const MCTargetOptions &Options)
+      : MCTargetAsmParser(Options, sti, MII), Parser(parser) {
     MCAsmParserExtension::Initialize(Parser);
 
     // Alias the .word directive to .short.
     parser.addAliasForDirective(".word", ".short");
 
     // Initialize the set of available features.
-    setAvailableFeatures(ComputeAvailableFeatures(getSTI().getFeatureBits()));
+    CurrentFeatures = sti.getFeatureBits();
+    setAvailableFeatures(ComputeAvailableFeatures(CurrentFeatures));
   }
 
   // Override MCTargetAsmParser.
@@ -1382,17 +1395,35 @@ bool SystemZAsmParser::parseDirectiveMachine(SMLoc L) {
       Parser.getTok().isNot(AsmToken::String))
     return TokError("unexpected token in '.machine' directive");
 
-  StringRef CPU = Parser.getTok().getIdentifier();
+  StringRef Id = Parser.getTok().getIdentifier();
+
+  // Parse push and pop directives first
+  if (Id == "push") {
+    // Push the Current FeatureBitSet onto the stack.
+    MachineStack.push_back(CurrentFeatures);
+    getTargetStreamer().emitMachine("push");
+  } else if (Id == "pop") {
+    // If the Stack is not empty, pop the topmost FeatureBitset and use it.
+    if (MachineStack.empty())
+      return TokError("pop without corresponding push in '.machine' directive");
+    CurrentFeatures = MachineStack.back();
+    MachineStack.pop_back();
+    setAvailableFeatures(CurrentFeatures);
+    getTargetStreamer().emitMachine("pop");
+  } else {
+    // Try to interpret the Identifier as a CPU spec and derive the
+    // FeatureBitset from that.
+    MCSubtargetInfo &STI = copySTI();
+    STI.setDefaultFeatures(Id, /*TuneCPU*/ Id, "");
+    CurrentFeatures = STI.getFeatureBits();
+    setAvailableFeatures(ComputeAvailableFeatures(CurrentFeatures));
+    getTargetStreamer().emitMachine(Id);
+  }
+
   Parser.Lex();
   if (parseEOL())
     return true;
 
-  MCSubtargetInfo &STI = copySTI();
-  STI.setDefaultFeatures(CPU, /*TuneCPU*/ CPU, "");
-  setAvailableFeatures(ComputeAvailableFeatures(STI.getFeatureBits()));
-
-  getTargetStreamer().emitMachine(CPU);
-
   return false;
 }
 

llvm/lib/Target/SystemZ/MCTargetDesc/SystemZTargetStreamer.h

@@ -54,7 +54,7 @@ class SystemZTargetStreamer : public MCTargetStreamer {
 
   void emitConstantPools() override;
 
-  virtual void emitMachine(StringRef CPU) {};
+  virtual void emitMachine(StringRef CPUOrCommand) {};
 
   virtual void emitExtern(StringRef Str) {};
 
@@ -85,7 +85,7 @@ class SystemZTargetHLASMStreamer : public SystemZTargetStreamer {
 class SystemZTargetELFStreamer : public SystemZTargetStreamer {
 public:
   SystemZTargetELFStreamer(MCStreamer &S) : SystemZTargetStreamer(S) {}
-  void emitMachine(StringRef CPU) override {}
+  void emitMachine(StringRef CPUOrCommand) override {}
 };
 
 class SystemZTargetGNUStreamer : public SystemZTargetStreamer {
@@ -94,8 +94,8 @@ class SystemZTargetGNUStreamer : public SystemZTargetStreamer {
 public:
   SystemZTargetGNUStreamer(MCStreamer &S, formatted_raw_ostream &OS)
       : SystemZTargetStreamer(S), OS(OS) {}
-  void emitMachine(StringRef CPU) override {
-    OS << "\t.machine " << CPU << "\n";
+  void emitMachine(StringRef CPUOrCommand) override {
+    OS << "\t.machine " << CPUOrCommand << "\n";
   }
 };
 

llvm/test/MC/SystemZ/machine-directive-invalid.s

@@ -1,10 +1,14 @@
+// NOTE: Assertions have been autogenerated by utils/update_mc_test_checks.py UTC_ARGS: --version 5
 # RUN: not llvm-mc -triple=s390x %s 2>&1 | FileCheck %s
 
-# CHECK: [[#@LINE+1]]:9: error: unexpected token in '.machine' directive
 .machine
+// CHECK: :[[@LINE-1]]:9: error: unexpected token in '.machine' directive
+
+.machine pop
+// CHECK: :[[@LINE-1]]:10: error: pop without corresponding push in '.machine' directive
 
-# CHECK: [[#@LINE+1]]:10: error: unexpected token in '.machine' directive
 .machine 42
+// CHECK: :[[@LINE-1]]:10: error: unexpected token in '.machine' directive
 
-# CHECK: [[#@LINE+1]]:13: error: expected newline
 .machine z13+
+// CHECK: :[[@LINE-1]]:13: error: expected newline

llvm/test/MC/SystemZ/machine-directive.s

@@ -5,16 +5,20 @@
 # CHECK: ^
 	
 # CHECK-NOT: error:
+# CHECK: .machine push
 # CHECK: .machine z13
 # CHECK: vgbm	%v0, 0
 # CHECK: .machine zEC12
-# CHECK: .machine z13
+# CHECK: .machine pop
 # CHECK: vgbm	%v0, 3
+# CHECK: .machine pop
 
+.machine push
 .machine z13
+.machine push
 vgbm    %v0, 0
 .machine zEC12
 vgbm    %v0, 1
-.machine z13
+.machine pop
 vgbm    %v0, 3
-
+.machine pop