Move this file from lib/Transforms/Scalar

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17544 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 136 insertions, 0 deletions

diff --git a/lib/Target/SparcV9/DecomposeMultiDimRefs.cpp b/lib/Target/SparcV9/DecomposeMultiDimRefs.cpp
new file mode 100644
index 0000000000..40e1be5d46
--- /dev/null
+++ b/lib/Target/SparcV9/DecomposeMultiDimRefs.cpp
@@ -0,0 +1,136 @@
+//===- llvm/Transforms/DecomposeMultiDimRefs.cpp - Lower array refs to 1D -===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+// DecomposeMultiDimRefs - Convert multi-dimensional references consisting of
+// any combination of 2 or more array and structure indices into a sequence of
+// instructions (using getelementpr and cast) so that each instruction has at
+// most one index (except structure references, which need an extra leading
+// index of [0]).
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Constants.h"
+#include "llvm/Constant.h"
+#include "llvm/Instructions.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/Debug.h"
+using namespace llvm;
+
+namespace {
+  Statistic<> NumAdded("lowerrefs", "# of getelementptr instructions added");
+
+  struct DecomposePass : public BasicBlockPass {
+    virtual bool runOnBasicBlock(BasicBlock &BB);
+  };
+  RegisterOpt<DecomposePass> X("lowerrefs", "Decompose multi-dimensional "
+                               "structure/array references");
+}
+
+// runOnBasicBlock - Entry point for array or structure references with multiple
+// indices.
+//
+bool DecomposePass::runOnBasicBlock(BasicBlock &BB) {
+  bool changed = false;
+  for (BasicBlock::iterator II = BB.begin(); II != BB.end(); )
+    if (GetElementPtrInst *gep = dyn_cast<GetElementPtrInst>(II++)) // pre-inc
+      if (gep->getNumIndices() >= 2)
+        changed |= DecomposeArrayRef(gep); // always modifies II
+  return changed;
+}
+
+FunctionPass *llvm::createDecomposeMultiDimRefsPass() {
+  return new DecomposePass();
+}
+
+static inline bool isZeroConst (Value *V) {
+  return isa<Constant> (V) && (cast<Constant>(V)->isNullValue());
+}
+
+// Function: DecomposeArrayRef()
+//  
+// For any GetElementPtrInst with 2 or more array and structure indices:
+// 
+//      opCode CompositeType* P, [uint|ubyte] idx1, ..., [uint|ubyte] idxN
+// 
+// this function generates the following sequence:
+// 
+//      ptr1   = getElementPtr P,         idx1
+//      ptr2   = getElementPtr ptr1,   0, idx2
+//      ...
+//      ptrN-1 = getElementPtr ptrN-2, 0, idxN-1
+//      opCode                 ptrN-1, 0, idxN  // New-MAI
+// 
+// Then it replaces the original instruction with this sequence,
+// and replaces all uses of the original instruction with New-MAI.
+// If idx1 is 0, we simply omit the first getElementPtr instruction.
+// 
+// On return: BBI points to the instruction after the current one
+//            (whether or not *BBI was replaced).
+// 
+// Return value: true if the instruction was replaced; false otherwise.
+// 
+bool llvm::DecomposeArrayRef(GetElementPtrInst* GEP) {
+  if (GEP->getNumIndices() < 2
+      || (GEP->getNumIndices() == 2
+          && isZeroConst(GEP->getOperand(1)))) {
+    DEBUG (std::cerr << "DecomposeArrayRef: Skipping " << *GEP);
+    return false;
+  } else {
+    DEBUG (std::cerr << "DecomposeArrayRef: Decomposing " << *GEP);
+  }
+
+  BasicBlock *BB = GEP->getParent();
+  Value *LastPtr = GEP->getPointerOperand();
+  Instruction *InsertPoint = GEP->getNext(); // Insert before the next insn
+
+  // Process each index except the last one.
+  User::const_op_iterator OI = GEP->idx_begin(), OE = GEP->idx_end();
+  for (; OI+1 != OE; ++OI) {
+    std::vector<Value*> Indices;
+    
+    // If this is the first index and is 0, skip it and move on!
+    if (OI == GEP->idx_begin()) {
+      if (isZeroConst (*OI))
+        continue;
+    }
+    else // Not the first index: include initial [0] to deref the last ptr
+      Indices.push_back(Constant::getNullValue(Type::LongTy));
+
+    Indices.push_back(*OI);
+
+    // New Instruction: nextPtr1 = GetElementPtr LastPtr, Indices
+    LastPtr = new GetElementPtrInst(LastPtr, Indices, "ptr1", InsertPoint);
+    ++NumAdded;
+  }
+
+  // Now create a new instruction to replace the original one
+  //
+  const PointerType *PtrTy = cast<PointerType>(LastPtr->getType());
+
+  // Get the final index vector, including an initial [0] as before.
+  std::vector<Value*> Indices;
+  Indices.push_back(Constant::getNullValue(Type::LongTy));
+  Indices.push_back(*OI);
+
+  Value *NewVal = new GetElementPtrInst(LastPtr, Indices, GEP->getName(),
+                                        InsertPoint);
+
+  // Replace all uses of the old instruction with the new
+  GEP->replaceAllUsesWith(NewVal);
+
+  // Now remove and delete the old instruction...
+  BB->getInstList().erase(GEP);
+
+  return true;
+}
+