Add new Pass infrastructure and some examples

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@836 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/HoistPHIConstants.cpp

@@ -0,0 +1,61 @@
+//===- llvm/Transforms/HoistPHIConstants.h - Normalize PHI nodes ------------=//
+//
+// HoistPHIConstants - Remove literal constants that are arguments of PHI nodes
+// by inserting cast instructions in the preceeding basic blocks, and changing
+// constant references into references of the casted value.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/HoistPHIConstants.h"
+#include "llvm/iOther.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/Method.h"
+#include <map>
+
+typedef pair<BasicBlock *, Value*> BBConstTy;
+typedef map<BBConstTy, CastInst *> CachedCopyMap;
+
+static Value *NormalizePhiOperand(PHINode *PN, Value *CPV,
+                                  BasicBlock *Pred, CachedCopyMap &CopyCache) {
+  
+  // Check if we've already inserted a copy for this constant in Pred
+  // Note that `copyCache[Pred]' will create an empty vector the first time
+  //
+  CachedCopyMap::iterator CCI = CopyCache.find(BBConstTy(Pred, CPV));
+  if (CCI != CopyCache.end()) return CCI->second;
+  
+  // Create a copy instruction and add it to the cache...
+  CastInst *Inst = new CastInst(CPV, CPV->getType());
+  CopyCache.insert(make_pair(BBConstTy(Pred, CPV), Inst));
+    
+  // Insert the copy just before the terminator inst of the predecessor BB
+  assert(Pred->getTerminator() && "Degenerate BB encountered!");
+  Pred->getInstList().insert(Pred->getInstList().end()-1, Inst);
+  
+  return Inst;
+}
+
+
+//---------------------------------------------------------------------------
+// Entry point for normalizing constant args in PHIs
+//---------------------------------------------------------------------------
+
+bool HoistPHIConstants::doPerMethodWork(Method *M) {
+  CachedCopyMap Cache;
+  
+  for (Method::iterator BI = M->begin(), BE = M->end(); BI != BE; ++BI)
+    for (BasicBlock::iterator II = (*BI)->begin(); II != (*BI)->end(); ++II) {
+      Instruction *Inst = *II;
+      if (!isa<PHINode>(Inst)) break;   // All PHIs occur at top of BB!
+      
+      PHINode *PN = cast<PHINode>(Inst);
+      for (unsigned i = 0; i < PN->getNumIncomingValues(); ++i) {
+        Value *Op = PN->getIncomingValue(i);
+        if (isa<ConstPoolVal>(Op))
+          PN->setIncomingValue(i,
+                NormalizePhiOperand(PN, Op, PN->getIncomingBlock(i), Cache));
+      }
+    }
+
+  return false;
+}