[llvm-commits] CVS: llvm/lib/Transforms/Scalar/InstructionCombining.cpp

[Chris Lattner]

Changes in directory llvm/lib/Transforms/Scalar:

InstructionCombining.cpp updated: 1.464 -> 1.465
---
Log message:

Turn casts into getelementptr's when possible.  This enables SROA to be more
aggressive in some cases where LLVMGCC 4 is inserting casts for no reason.

This implements InstCombine/cast.ll:test27/28.



---
Diffs of the changes:  (+23 -0)

 InstructionCombining.cpp |   23 +++++++++++++++++++++++
 1 files changed, 23 insertions(+)


Index: llvm/lib/Transforms/Scalar/InstructionCombining.cpp
diff -u llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.464 llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.465
--- llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.464	Mon Apr 10 18:06:36 2006
+++ llvm/lib/Transforms/Scalar/InstructionCombining.cpp	Wed Apr 12 13:09:35 2006
@@ -4813,7 +4813,30 @@
   if (isa<PHINode>(Src))
     if (Instruction *NV = FoldOpIntoPhi(CI))
       return NV;
+  
+  // If the source and destination are pointers, and this cast is equivalent to
+  // a getelementptr X, 0, 0, 0...  turn it into the appropriate getelementptr.
+  // This can enhance SROA and other transforms that want type-safe pointers.
+  if (const PointerType *DstPTy = dyn_cast<PointerType>(CI.getType()))
+    if (const PointerType *SrcPTy = dyn_cast<PointerType>(Src->getType())) {
+      const Type *DstTy = DstPTy->getElementType();
+      const Type *SrcTy = SrcPTy->getElementType();
+      
+      Constant *ZeroUInt = Constant::getNullValue(Type::UIntTy);
+      unsigned NumZeros = 0;
+      while (SrcTy != DstTy && 
+             isa<CompositeType>(SrcTy) && !isa<PointerType>(SrcTy)) {
+        SrcTy = cast<CompositeType>(SrcTy)->getTypeAtIndex(ZeroUInt);
+        ++NumZeros;
+      }
 
+      // If we found a path from the src to dest, create the getelementptr now.
+      if (SrcTy == DstTy) {
+        std::vector<Value*> Idxs(NumZeros+1, ZeroUInt);
+        return new GetElementPtrInst(Src, Idxs);
+      }
+    }
+      
   // If the source value is an instruction with only this use, we can attempt to
   // propagate the cast into the instruction.  Also, only handle integral types
   // for now.