1 files changed, 112 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/CodeGenLICM.cpp b/lib/Transforms/Scalar/CodeGenLICM.cpp
new file mode 100644
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--- /dev/null
+++ b/lib/Transforms/Scalar/CodeGenLICM.cpp
@@ -0,0 +1,112 @@
+//===- CodeGenLICM.cpp - LICM a function for code generation --------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This function performs late LICM, hoisting constants out of loops that
+// are not valid immediates. It should not be followed by instcombine,
+// because instcombine would quickly stuff the constants back into the loop.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "codegen-licm"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Instructions.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/LLVMContext.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/ADT/DenseMap.h"
+using namespace llvm;
+
+namespace {
+  class CodeGenLICM : public LoopPass {
+    virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const;
+  public:
+    static char ID; // Pass identification, replacement for typeid
+    explicit CodeGenLICM() : LoopPass(&ID) {}
+  };
+}
+
+char CodeGenLICM::ID = 0;
+static RegisterPass<CodeGenLICM> X("codegen-licm",
+                                   "hoist constants out of loops");
+
+Pass *llvm::createCodeGenLICMPass() {
+  return new CodeGenLICM();
+}
+
+bool CodeGenLICM::runOnLoop(Loop *L, LPPassManager &) {
+  bool Changed = false;
+
+  // Only visit outermost loops.
+  if (L->getParentLoop()) return Changed;
+
+  Instruction *PreheaderTerm = L->getLoopPreheader()->getTerminator();
+  DenseMap<Constant *, BitCastInst *> HoistedConstants;
+
+  for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
+       I != E; ++I) {
+    BasicBlock *BB = *I;
+    for (BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
+         BBI != BBE; ++BBI) {
+      Instruction *I = BBI;
+      // TODO: For now, skip all intrinsic instructions, because some of them
+      // can require their operands to be constants, and we don't want to
+      // break that.
+      if (isa<IntrinsicInst>(I))
+        continue;
+      // LLVM represents fneg as -0.0-x; don't hoist the -0.0 out.
+      if (BinaryOperator::isFNeg(I) ||
+          BinaryOperator::isNeg(I) ||
+          BinaryOperator::isNot(I))
+        continue;
+      for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
+        // Don't hoist out switch case constants.
+        if (isa<SwitchInst>(I) && i == 1)
+          break;
+        // Don't hoist out shuffle masks.
+        if (isa<ShuffleVectorInst>(I) && i == 2)
+          break;
+        Value *Op = I->getOperand(i);
+        Constant *C = dyn_cast<Constant>(Op);
+        if (!C) continue;
+        // TODO: Ask the target which constants are legal. This would allow
+        // us to add support for hoisting ConstantInts and GlobalValues too.
+        if (isa<ConstantFP>(C) ||
+            isa<ConstantVector>(C) ||
+            isa<ConstantAggregateZero>(C)) {
+          BitCastInst *&BC = HoistedConstants[C];
+          if (!BC)
+            BC = new BitCastInst(C, C->getType(), "hoist", PreheaderTerm);
+          I->setOperand(i, BC);
+          Changed = true;
+        }
+      }
+    }
+  }
+
+  return Changed;
+}
+
+void CodeGenLICM::getAnalysisUsage(AnalysisUsage &AU) const {
+  // This pass preserves just about everything. List some popular things here.
+  AU.setPreservesCFG();
+  AU.addPreservedID(LoopSimplifyID);
+  AU.addPreserved<LoopInfo>();
+  AU.addPreserved<AliasAnalysis>();
+  AU.addPreserved("scalar-evolution");
+  AU.addPreserved("iv-users");
+  AU.addPreserved("lda");
+  AU.addPreserved("live-values");
+
+  // Hoisting requires a loop preheader.
+  AU.addRequiredID(LoopSimplifyID);
+}