Add code pulled out of TransformInternals.cpp, ConstProp.cpp, and DCE.cpp

llvm-svn: 2513

3 files changed, 196 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
new file mode 100644
index 00000000000..89078a12e95
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -0,0 +1,79 @@
+//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
+//
+// This family of functions perform manipulations on basic blocks, and
+// instructions contained within basic blocks.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Function.h"
+#include "llvm/Instruction.h"
+#include <algorithm>
+
+// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
+// with a value, then remove and delete the original instruction.
+//
+void ReplaceInstWithValue(BasicBlock::InstListType &BIL,
+                          BasicBlock::iterator &BI, Value *V) {
+  Instruction *I = *BI;
+  // Replaces all of the uses of the instruction with uses of the value
+  I->replaceAllUsesWith(V);
+
+  // Remove the unneccesary instruction now...
+  BIL.remove(BI);
+
+  // Make sure to propogate a name if there is one already...
+  if (I->hasName() && !V->hasName())
+    V->setName(I->getName(), BIL.getParent()->getSymbolTable());
+
+  // Remove the dead instruction now...
+  delete I;
+}
+
+
+// ReplaceInstWithInst - Replace the instruction specified by BI with the
+// instruction specified by I.  The original instruction is deleted and BI is
+// updated to point to the new instruction.
+//
+void ReplaceInstWithInst(BasicBlock::InstListType &BIL,
+                         BasicBlock::iterator &BI, Instruction *I) {
+  assert(I->getParent() == 0 &&
+         "ReplaceInstWithInst: Instruction already inserted into basic block!");
+
+  // Insert the new instruction into the basic block...
+  BI = BIL.insert(BI, I)+1;  // Increment BI to point to instruction to delete
+
+  // Replace all uses of the old instruction, and delete it.
+  ReplaceInstWithValue(BIL, BI, I);
+
+  // Move BI back to point to the newly inserted instruction
+  --BI;
+}
+
+// ReplaceInstWithInst - Replace the instruction specified by From with the
+// instruction specified by To.  Note that this is slower than providing an
+// iterator directly, because the basic block containing From must be searched
+// for the instruction.
+//
+void ReplaceInstWithInst(Instruction *From, Instruction *To) {
+  BasicBlock *BB = From->getParent();
+  BasicBlock::InstListType &BIL = BB->getInstList();
+  BasicBlock::iterator BI = find(BIL.begin(), BIL.end(), From);
+  assert(BI != BIL.end() && "Inst not in it's parents BB!");
+  ReplaceInstWithInst(BIL, BI, To);
+}
+
+// InsertInstBeforeInst - Insert 'NewInst' into the basic block that 'Existing'
+// is already in, and put it right before 'Existing'.  This instruction should
+// only be used when there is no iterator to Existing already around.  The 
+// returned iterator points to the new instruction.
+//
+BasicBlock::iterator InsertInstBeforeInst(Instruction *NewInst,
+                                          Instruction *Existing) {
+  BasicBlock *BB = Existing->getParent();
+  BasicBlock::InstListType &BIL = BB->getInstList();
+  BasicBlock::iterator BI = find(BIL.begin(), BIL.end(), Existing);
+  assert(BI != BIL.end() && "Inst not in it's parents BB!");
+  return BIL.insert(BI, NewInst);
+}
+
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
new file mode 100644
index 00000000000..36622642bfa
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -0,0 +1,111 @@
+//===-- Local.cpp - Functions to perform local transformations ------------===//
+//
+// This family of functions perform various local transformations to the
+// program.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/iTerminators.h"
+#include "llvm/ConstantHandling.h"
+
+//===----------------------------------------------------------------------===//
+//  Local constant propogation...
+//
+
+// ConstantFoldInstruction - If an instruction references constants, try to fold
+// them together...
+//
+bool doConstantPropogation(BasicBlock *BB, BasicBlock::iterator &II) {
+  Instruction *Inst = *II;
+  if (Constant *C = ConstantFoldInstruction(Inst)) {
+    // Replaces all of the uses of a variable with uses of the constant.
+    Inst->replaceAllUsesWith(C);
+    
+    // Remove the instruction from the basic block...
+    delete BB->getInstList().remove(II);
+    return true;
+  }
+
+  return false;
+}
+
+// ConstantFoldTerminator - If a terminator instruction is predicated on a
+// constant value, convert it into an unconditional branch to the constant
+// destination.
+//
+bool ConstantFoldTerminator(BasicBlock *BB, BasicBlock::iterator &II,
+                            TerminatorInst *T) {
+  // Branch - See if we are conditional jumping on constant
+  if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
+    if (BI->isUnconditional()) return false;  // Can't optimize uncond branch
+    BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
+    BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
+
+    if (ConstantBool *Cond = dyn_cast<ConstantBool>(BI->getCondition())) {
+      // Are we branching on constant?
+      // YES.  Change to unconditional branch...
+      BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
+      BasicBlock *OldDest     = Cond->getValue() ? Dest2 : Dest1;
+
+      //cerr << "Function: " << T->getParent()->getParent() 
+      //     << "\nRemoving branch from " << T->getParent() 
+      //     << "\n\nTo: " << OldDest << endl;
+
+      // Let the basic block know that we are letting go of it.  Based on this,
+      // it will adjust it's PHI nodes.
+      assert(BI->getParent() && "Terminator not inserted in block!");
+      OldDest->removePredecessor(BI->getParent());
+
+      // Set the unconditional destination, and change the insn to be an
+      // unconditional branch.
+      BI->setUnconditionalDest(Destination);
+      II = BB->end()-1;  // Update instruction iterator!
+      return true;
+    }
+#if 0
+    // FIXME: TODO: This doesn't work if the destination has PHI nodes with
+    // different incoming values on each branch!
+    //
+    else if (Dest2 == Dest1) {       // Conditional branch to same location?
+      // This branch matches something like this:  
+      //     br bool %cond, label %Dest, label %Dest
+      // and changes it into:  br label %Dest
+
+      // Let the basic block know that we are letting go of one copy of it.
+      assert(BI->getParent() && "Terminator not inserted in block!");
+      Dest1->removePredecessor(BI->getParent());
+
+      // Change a conditional branch to unconditional.
+      BI->setUnconditionalDest(Dest1);
+      return true;
+    }
+#endif
+  }
+  return false;
+}
+
+
+
+//===----------------------------------------------------------------------===//
+//  Local dead code elimination...
+//
+
+bool isInstructionTriviallyDead(Instruction *I) {
+  return I->use_empty() && !I->hasSideEffects() && !isa<TerminatorInst>(I);
+}
+
+// dceInstruction - Inspect the instruction at *BBI and figure out if it's
+// [trivially] dead.  If so, remove the instruction and update the iterator
+// to point to the instruction that immediately succeeded the original
+// instruction.
+//
+bool dceInstruction(BasicBlock::InstListType &BBIL,
+                    BasicBlock::iterator &BBI) {
+  // Look for un"used" definitions...
+  if (isInstructionTriviallyDead(*BBI)) {
+    delete BBIL.remove(BBI);   // Bye bye
+    return true;
+  }
+  return false;
+}
diff --git a/llvm/lib/Transforms/Utils/Makefile b/llvm/lib/Transforms/Utils/Makefile
new file mode 100644
index 00000000000..f451df2d5c2
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/Makefile
@@ -0,0 +1,6 @@
+LEVEL = ../../..
+
+LIBRARYNAME = transformutils
+
+include $(LEVEL)/Makefile.common
+