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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2513 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 111 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
new file mode 100644
index 0000000000..36622642bf
--- /dev/null
+++ b/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;
+}