R600: New control flow for SI v2

This patch replaces the control flow handling with a new
pass which structurize the graph before transforming it to
machine instruction. This has a couple of different advantages
and currently fixes 20 piglit tests without a single regression.

It is now a general purpose transformation that could be not
only be used for SI/R6xx, but also for other hardware
implementations that use a form of structurized control flow.

v2: further cleanup, fixes and documentation

Patch by: Christian König

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
Tested-by: Michel Dänzer <michel.daenzer@amd.com>
llvm-svn: 170591

1 files changed, 337 insertions, 0 deletions

diff --git a/llvm/lib/Target/R600/SIAnnotateControlFlow.cpp b/llvm/lib/Target/R600/SIAnnotateControlFlow.cpp
new file mode 100644
index 00000000000..d13183557d2
--- /dev/null
+++ b/llvm/lib/Target/R600/SIAnnotateControlFlow.cpp
@@ -0,0 +1,337 @@
+//===-- SIAnnotateControlFlow.cpp -  ------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+/// Annotates the control flow with hardware specific intrinsics.
+//
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPU.h"
+
+#include "llvm/Pass.h"
+#include "llvm/Module.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/ADT/DepthFirstIterator.h"
+#include "llvm/Transforms/Utils/SSAUpdater.h"
+
+using namespace llvm;
+
+namespace {
+
+// Complex types used in this pass
+typedef std::pair<BasicBlock *, Value *> StackEntry;
+typedef SmallVector<StackEntry, 16> StackVector;
+
+// Intrinsic names the control flow is annotated with
+static const char *IfIntrinsic = "llvm.SI.if";
+static const char *ElseIntrinsic = "llvm.SI.else";
+static const char *BreakIntrinsic = "llvm.SI.break";
+static const char *IfBreakIntrinsic = "llvm.SI.if.break";
+static const char *ElseBreakIntrinsic = "llvm.SI.else.break";
+static const char *LoopIntrinsic = "llvm.SI.loop";
+static const char *EndCfIntrinsic = "llvm.SI.end.cf";
+
+class SIAnnotateControlFlow : public FunctionPass {
+
+  static char ID;
+
+  Type *Boolean;
+  Type *Void;
+  Type *Int64;
+  Type *ReturnStruct;
+
+  ConstantInt *BoolTrue;
+  ConstantInt *BoolFalse;
+  UndefValue *BoolUndef;
+  Constant *Int64Zero;
+
+  Constant *If;
+  Constant *Else;
+  Constant *Break;
+  Constant *IfBreak;
+  Constant *ElseBreak;
+  Constant *Loop;
+  Constant *EndCf;
+
+  DominatorTree *DT;
+  StackVector Stack;
+  SSAUpdater PhiInserter;
+
+  bool isTopOfStack(BasicBlock *BB);
+
+  Value *popSaved();
+
+  void push(BasicBlock *BB, Value *Saved);
+
+  bool isElse(PHINode *Phi);
+
+  void eraseIfUnused(PHINode *Phi);
+
+  void openIf(BranchInst *Term);
+
+  void insertElse(BranchInst *Term);
+
+  void handleLoopCondition(Value *Cond);
+
+  void handleLoop(BranchInst *Term);
+
+  void closeControlFlow(BasicBlock *BB);
+
+public:
+  SIAnnotateControlFlow():
+    FunctionPass(ID) { }
+
+  virtual bool doInitialization(Module &M);
+
+  virtual bool runOnFunction(Function &F);
+
+  virtual const char *getPassName() const {
+    return "SI annotate control flow";
+  }
+
+  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+
+    AU.addRequired<DominatorTree>();
+    AU.addPreserved<DominatorTree>();
+    FunctionPass::getAnalysisUsage(AU);
+  }
+
+};
+
+} // end anonymous namespace
+
+char SIAnnotateControlFlow::ID = 0;
+
+/// \brief Initialize all the types and constants used in the pass
+bool SIAnnotateControlFlow::doInitialization(Module &M) {
+
+  LLVMContext &Context = M.getContext();
+
+  Void = Type::getVoidTy(Context);
+  Boolean = Type::getInt1Ty(Context);
+  Int64 = Type::getInt64Ty(Context);
+  ReturnStruct = StructType::get(Boolean, Int64, (Type *)0);
+
+  BoolTrue = ConstantInt::getTrue(Context);
+  BoolFalse = ConstantInt::getFalse(Context);
+  BoolUndef = UndefValue::get(Boolean);
+  Int64Zero = ConstantInt::get(Int64, 0);
+
+  If = M.getOrInsertFunction(
+    IfIntrinsic, ReturnStruct, Boolean, (Type *)0);
+
+  Else = M.getOrInsertFunction(
+    ElseIntrinsic, ReturnStruct, Int64, (Type *)0);
+
+  Break = M.getOrInsertFunction(
+    BreakIntrinsic, Int64, Int64, (Type *)0);
+
+  IfBreak = M.getOrInsertFunction(
+    IfBreakIntrinsic, Int64, Boolean, Int64, (Type *)0);
+
+  ElseBreak = M.getOrInsertFunction(
+    ElseBreakIntrinsic, Int64, Int64, Int64, (Type *)0);
+
+  Loop = M.getOrInsertFunction(
+    LoopIntrinsic, Boolean, Int64, (Type *)0);
+
+  EndCf = M.getOrInsertFunction(
+    EndCfIntrinsic, Void, Int64, (Type *)0);
+
+  return false;
+}
+
+/// \brief Is BB the last block saved on the stack ?
+bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
+  return Stack.back().first == BB;
+}
+
+/// \brief Pop the last saved value from the control flow stack
+Value *SIAnnotateControlFlow::popSaved() {
+  return Stack.pop_back_val().second;
+}
+
+/// \brief Push a BB and saved value to the control flow stack
+void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
+  Stack.push_back(std::make_pair(BB, Saved));
+}
+
+/// \brief Can the condition represented by this PHI node treated like
+/// an "Else" block?
+bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
+
+  BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
+  for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
+    if (Phi->getIncomingBlock(i) == IDom) {
+
+      if (Phi->getIncomingValue(i) != BoolTrue)
+        return false;
+
+    } else {
+      if (Phi->getIncomingValue(i) != BoolFalse)
+        return false;
+ 
+    }
+  }
+  return true;
+}
+
+// \brief Erase "Phi" if it is not used any more
+void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
+  if (!Phi->hasNUsesOrMore(1))
+    Phi->eraseFromParent();
+}
+
+/// \brief Open a new "If" block
+void SIAnnotateControlFlow::openIf(BranchInst *Term) {
+  Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
+  Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
+  push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
+}
+
+/// \brief Close the last "If" block and open a new "Else" block
+void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
+  Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
+  Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
+  push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
+}
+
+/// \brief Recursively handle the condition leading to a loop
+void SIAnnotateControlFlow::handleLoopCondition(Value *Cond) {
+
+  if (PHINode *Phi = dyn_cast<PHINode>(Cond)) {
+
+    // Handle all non constant incoming values first
+    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
+      Value *Incoming = Phi->getIncomingValue(i);
+      if (isa<ConstantInt>(Incoming))
+        continue;
+
+      Phi->setIncomingValue(i, BoolFalse);
+      handleLoopCondition(Incoming);
+    }
+
+    BasicBlock *Parent = Phi->getParent();
+    BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();
+
+    for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
+
+      Value *Incoming = Phi->getIncomingValue(i);
+      if (Incoming != BoolTrue)
+        continue;
+
+      BasicBlock *From = Phi->getIncomingBlock(i);
+      if (From == IDom) {
+        CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
+        if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
+          Value *Args[] = {
+            OldEnd->getArgOperand(0),
+            PhiInserter.GetValueAtEndOfBlock(Parent)
+          };
+          Value *Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
+          PhiInserter.AddAvailableValue(Parent, Ret);
+          continue;
+        }
+      }
+
+      TerminatorInst *Insert = From->getTerminator();
+      Value *Arg = PhiInserter.GetValueAtEndOfBlock(From);
+      Value *Ret = CallInst::Create(Break, Arg, "", Insert);
+      PhiInserter.AddAvailableValue(From, Ret);
+    }
+    eraseIfUnused(Phi);
+
+  } else if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
+    BasicBlock *Parent = Inst->getParent();
+    TerminatorInst *Insert = Parent->getTerminator();
+    Value *Args[] = { Cond, PhiInserter.GetValueAtEndOfBlock(Parent) };
+    Value *Ret = CallInst::Create(IfBreak, Args, "", Insert);
+    PhiInserter.AddAvailableValue(Parent, Ret);
+
+  } else {
+    assert(0 && "Unhandled loop condition!");
+  }
+}
+
+/// \brief Handle a back edge (loop)
+void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
+
+  BasicBlock *Target = Term->getSuccessor(1);
+  PHINode *Broken = PHINode::Create(Int64, 0, "", &Target->front());
+
+  PhiInserter.Initialize(Int64, "");
+  PhiInserter.AddAvailableValue(Target, Broken);
+
+  Value *Cond = Term->getCondition();
+  Term->setCondition(BoolTrue);
+  handleLoopCondition(Cond);
+
+  BasicBlock *BB = Term->getParent();
+  Value *Arg = PhiInserter.GetValueAtEndOfBlock(BB);
+  for (pred_iterator PI = pred_begin(Target), PE = pred_end(Target);
+       PI != PE; ++PI) {
+
+    Broken->addIncoming(*PI == BB ? Arg : Int64Zero, *PI);
+  }
+
+  Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
+  push(Term->getSuccessor(0), Arg);
+}
+
+/// \brief Close the last opened control flow
+void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
+  CallInst::Create(EndCf, popSaved(), "", BB->getFirstInsertionPt());
+}
+
+/// \brief Annotate the control flow with intrinsics so the backend can
+/// recognize if/then/else and loops.
+bool SIAnnotateControlFlow::runOnFunction(Function &F) {
+
+  DT = &getAnalysis<DominatorTree>();
+
+  for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
+       E = df_end(&F.getEntryBlock()); I != E; ++I) {
+
+    BranchInst *Term = dyn_cast<BranchInst>((*I)->getTerminator());
+
+    if (!Term || Term->isUnconditional()) {
+      if (isTopOfStack(*I))
+        closeControlFlow(*I);
+      continue;
+    }
+
+    if (I.nodeVisited(Term->getSuccessor(1))) {
+      if (isTopOfStack(*I))
+        closeControlFlow(*I);
+      handleLoop(Term);
+      continue;
+    }
+
+    if (isTopOfStack(*I)) {
+      PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
+      if (Phi && Phi->getParent() == *I && isElse(Phi)) {
+        insertElse(Term);
+        eraseIfUnused(Phi);
+        continue;
+      }
+      closeControlFlow(*I);
+    }
+    openIf(Term);
+  }
+
+  assert(Stack.empty());
+  return true;
+}
+
+/// \brief Create the annotation pass
+FunctionPass *llvm::createSIAnnotateControlFlowPass() {
+
+  return new SIAnnotateControlFlow();
+}