Teach ISel not to optimize 'optnone' functions (revised).

Improvements over r195317:
- Set/restore EnableFastISel flag instead of just running FastISel within
  SelectAllBasicBlocks; the flag is checked in various places, and
  FastISel won't run properly if those places don't do the right thing.
- Test looks for normal ISel versus FastISel behavior, and not
  something more subtle that doesn't work everywhere.

Based on work by Andrea Di Biagio.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195491 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCCodeGenInfo.h

@@ -42,6 +42,9 @@ namespace llvm {
     CodeModel::Model getCodeModel() const { return CMModel; }
 
     CodeGenOpt::Level getOptLevel() const { return OptLevel; }
+
+    // Allow overriding OptLevel on a per-function basis.
+    void setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
   };
 } // namespace llvm
 

include/llvm/Target/TargetMachine.h

@@ -75,7 +75,8 @@ protected: // Can only create subclasses.
   std::string TargetFS;
 
   /// CodeGenInfo - Low level target information such as relocation model.
-  const MCCodeGenInfo *CodeGenInfo;
+  /// Non-const to allow resetting optimization level per-function.
+  MCCodeGenInfo *CodeGenInfo;
 
   /// AsmInfo - Contains target specific asm information.
   ///
@@ -213,6 +214,9 @@ public:
   /// Default, or Aggressive.
   CodeGenOpt::Level getOptLevel() const;
 
+  /// \brief Overrides the optimization level.
+  void setOptLevel(CodeGenOpt::Level Level) const;
+
   void setFastISel(bool Enable) { Options.EnableFastISel = Enable; }
 
   bool shouldPrintMachineCode() const { return Options.PrintMachineCode; }

lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -222,6 +222,44 @@ defaultListDAGScheduler("default", "Best scheduler for the target",
                         createDefaultScheduler);
 
 namespace llvm {
+  //===--------------------------------------------------------------------===//
+  /// \brief This class is used by SelectionDAGISel to temporarily override
+  /// the optimization level on a per-function basis.
+  class OptLevelChanger {
+    SelectionDAGISel &IS;
+    CodeGenOpt::Level SavedOptLevel;
+    bool SavedFastISel;
+
+  public:
+    OptLevelChanger(SelectionDAGISel &ISel,
+                    CodeGenOpt::Level NewOptLevel) : IS(ISel) {
+      SavedOptLevel = IS.OptLevel;
+      if (NewOptLevel == SavedOptLevel)
+        return;
+      IS.OptLevel = NewOptLevel;
+      IS.TM.setOptLevel(NewOptLevel);
+      SavedFastISel = IS.TM.Options.EnableFastISel;
+      if (NewOptLevel == CodeGenOpt::None)
+        IS.TM.setFastISel(true);
+      DEBUG(dbgs() << "\nChanging optimization level for Function "
+            << IS.MF->getFunction()->getName() << "\n");
+      DEBUG(dbgs() << "\tBefore: -O" << SavedOptLevel
+            << " ; After: -O" << NewOptLevel << "\n");
+    }
+
+    ~OptLevelChanger() {
+      if (IS.OptLevel == SavedOptLevel)
+        return;
+      DEBUG(dbgs() << "\nRestoring optimization level for Function "
+            << IS.MF->getFunction()->getName() << "\n");
+      DEBUG(dbgs() << "\tBefore: -O" << IS.OptLevel
+            << " ; After: -O" << SavedOptLevel << "\n");
+      IS.OptLevel = SavedOptLevel;
+      IS.TM.setOptLevel(SavedOptLevel);
+      IS.TM.setFastISel(SavedFastISel);
+    }
+  };
+
   //===--------------------------------------------------------------------===//
   /// createDefaultScheduler - This creates an instruction scheduler appropriate
   /// for the target.
@@ -370,6 +408,12 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
   ST.resetSubtargetFeatures(MF);
   TM.resetTargetOptions(MF);
 
+  // Reset OptLevel to None for optnone functions.
+  CodeGenOpt::Level NewOptLevel = OptLevel;
+  if (Fn.hasFnAttribute(Attribute::OptimizeNone))
+    NewOptLevel = CodeGenOpt::None;
+  OptLevelChanger OLC(*this, NewOptLevel);
+
   DEBUG(dbgs() << "\n\n\n=== " << Fn.getName() << "\n");
 
   SplitCriticalSideEffectEdges(const_cast<Function&>(Fn), this);

lib/Target/TargetMachine.cpp

@@ -164,6 +164,11 @@ CodeGenOpt::Level TargetMachine::getOptLevel() const {
   return CodeGenInfo->getOptLevel();
 }
 
+void TargetMachine::setOptLevel(CodeGenOpt::Level Level) const {
+  if (CodeGenInfo)
+    CodeGenInfo->setOptLevel(Level);
+}
+
 bool TargetMachine::getAsmVerbosityDefault() {
   return AsmVerbosityDefault;
 }

test/CodeGen/X86/isel-optnone.ll

@@ -0,0 +1,42 @@
+; RUN: llc -O2 -march=x86 < %s | FileCheck %s
+
+define i32* @fooOptnone(i32* %p, i32* %q, i32** %z) #0 {
+entry:
+  %r = load i32* %p
+  %s = load i32* %q
+  %y = load i32** %z
+
+  %t0 = add i32 %r, %s
+  %t1 = add i32 %t0, 1
+  %t2 = getelementptr i32* %y, i32 1
+  %t3 = getelementptr i32* %t2, i32 %t1
+
+  ret i32* %t3
+
+; 'optnone' should use fast-isel which will not produce 'lea'.
+; CHECK-LABEL: fooOptnone:
+; CHECK-NOT:   lea
+; CHECK:       ret
+}
+
+define i32* @fooNormal(i32* %p, i32* %q, i32** %z) #1 {
+entry:
+  %r = load i32* %p
+  %s = load i32* %q
+  %y = load i32** %z
+
+  %t0 = add i32 %r, %s
+  %t1 = add i32 %t0, 1
+  %t2 = getelementptr i32* %y, i32 1
+  %t3 = getelementptr i32* %t2, i32 %t1
+
+  ret i32* %t3
+
+; Normal ISel will produce 'lea'.
+; CHECK-LABEL: fooNormal:
+; CHECK:       lea
+; CHECK:       ret
+}
+
+attributes #0 = { nounwind optnone noinline }
+attributes #1 = { nounwind }