From c9978bab4bc4bafc2d2d2ca2c76f48c02c274df4 Mon Sep 17 00:00:00 2001
From: "Duncan P. N. Exon Smith" <dexonsmith@apple.com>
Date: Fri, 10 Jul 2015 22:52:15 +0000
Subject: [PATCH] MC: Only allow changing feature bits in MCSubtargetInfo

Disallow all mutation of `MCSubtargetInfo` expect the feature bits.

Besides deleting the assignment operators -- which were dead "code" --
this restricts `InitMCProcessorInfo()` to subclass initialization
sequences, and exposes a new more limited function called
`setDefaultFeatures()` for use by the ARMAsmParser `.cpu` directive.

There's a small functional change here: ARMAsmParser used to adjust
`MCSubtargetInfo::CPUSchedModel` as a side effect of calling
`InitMCProcessorInfo()`, but I've removed that suspicious behaviour.
Since the AsmParser shouldn't be doing any scheduling, there shouldn't
be any observable change...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241961 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/MC/MCSubtargetInfo.h         | 14 ++++++++++++--
 lib/MC/MCSubtargetInfo.cpp                | 17 ++++++++++++-----
 lib/Target/ARM/AsmParser/ARMAsmParser.cpp |  2 +-
 3 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/include/llvm/MC/MCSubtargetInfo.h b/include/llvm/MC/MCSubtargetInfo.h
index 36332a957ef..d5ad4eebf9e 100644
--- a/include/llvm/MC/MCSubtargetInfo.h
+++ b/include/llvm/MC/MCSubtargetInfo.h
@@ -45,8 +45,11 @@ class MCSubtargetInfo {
   FeatureBitset FeatureBits;           // Feature bits for current CPU + FS
 
   MCSubtargetInfo() = delete;
+  MCSubtargetInfo &operator=(MCSubtargetInfo &&) = delete;
+  MCSubtargetInfo &operator=(const MCSubtargetInfo &) = delete;
 
 public:
+  MCSubtargetInfo(const MCSubtargetInfo &) = default;
   MCSubtargetInfo(const Triple &TT, StringRef CPU, StringRef FS,
                   ArrayRef<SubtargetFeatureKV> PF,
                   ArrayRef<SubtargetFeatureKV> PD,
@@ -75,10 +78,17 @@ public:
     FeatureBits = FeatureBits_;
   }
 
-  /// InitMCProcessorInfo - Set or change the CPU (optionally supplemented with
-  /// feature string). Recompute feature bits and scheduling model.
+protected:
+  /// Initialize the scheduling model and feature bits.
+  ///
+  /// FIXME: Find a way to stick this in the constructor, since it should only
+  /// be called during initialization.
   void InitMCProcessorInfo(StringRef CPU, StringRef FS);
 
+public:
+  /// Set the features to the default for the given CPU.
+  void setDefaultFeatures(StringRef CPU);
+
   /// ToggleFeature - Toggle a feature and returns the re-computed feature
   /// bits. This version does not change the implied bits.
   FeatureBitset ToggleFeature(uint64_t FB);
diff --git a/lib/MC/MCSubtargetInfo.cpp b/lib/MC/MCSubtargetInfo.cpp
index 9dd551e4fc3..9210cf544b1 100644
--- a/lib/MC/MCSubtargetInfo.cpp
+++ b/lib/MC/MCSubtargetInfo.cpp
@@ -17,18 +17,25 @@
 
 using namespace llvm;
 
-/// InitMCProcessorInfo - Set or change the CPU (optionally supplemented
-/// with feature string). Recompute feature bits and scheduling model.
-void
-MCSubtargetInfo::InitMCProcessorInfo(StringRef CPU, StringRef FS) {
+static FeatureBitset getFeatures(StringRef CPU, StringRef FS,
+                                 ArrayRef<SubtargetFeatureKV> ProcDesc,
+                                 ArrayRef<SubtargetFeatureKV> ProcFeatures) {
   SubtargetFeatures Features(FS);
-  FeatureBits = Features.getFeatureBits(CPU, ProcDesc, ProcFeatures);
+  return Features.getFeatureBits(CPU, ProcDesc, ProcFeatures);
+}
+
+void MCSubtargetInfo::InitMCProcessorInfo(StringRef CPU, StringRef FS) {
+  FeatureBits = getFeatures(CPU, FS, ProcDesc, ProcFeatures);
   if (!CPU.empty())
     CPUSchedModel = &getSchedModelForCPU(CPU);
   else
     CPUSchedModel = &MCSchedModel::GetDefaultSchedModel();
 }
 
+void MCSubtargetInfo::setDefaultFeatures(StringRef CPU) {
+  FeatureBits = getFeatures(CPU, "", ProcDesc, ProcFeatures);
+}
+
 MCSubtargetInfo::MCSubtargetInfo(
     const Triple &TT, StringRef C, StringRef FS,
     ArrayRef<SubtargetFeatureKV> PF, ArrayRef<SubtargetFeatureKV> PD,
diff --git a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index 074c485023a..6245fa25deb 100644
--- a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -9212,7 +9212,7 @@ bool ARMAsmParser::parseDirectiveCPU(SMLoc L) {
     return false;
   }
 
-  STI.InitMCProcessorInfo(CPU, "");
+  STI.setDefaultFeatures(CPU);
   setAvailableFeatures(ComputeAvailableFeatures(STI.getFeatureBits()));
 
   return false;
-- 
2.34.1