6 files changed, 42 insertions, 12 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index af300fc3577b..fa7bb12ff218 100644
--- a/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1751,6 +1751,11 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
             return BinaryOperator::CreateOr(NotX, NotY);
           return BinaryOperator::CreateAnd(NotX, NotY);
         }
+
+      } else if (Op0I->getOpcode() == Instruction::AShr) {
+        // ~(~X >>s Y) --> (X >>s Y)
+        if (Value *Op0NotVal = dyn_castNotVal(Op0I->getOperand(0)))
+          return BinaryOperator::CreateAShr(Op0NotVal, Op0I->getOperand(1));
       }
     }
   }
diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index e018b351082a..f25dd3582b2e 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -955,6 +955,19 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
                                       ShAmt);
   }
 
+  // If this input is a trunc from our destination, then turn sext(trunc(x))
+  // into shifts.
+  if (TruncInst *TI = dyn_cast<TruncInst>(Src))
+    if (TI->hasOneUse() && TI->getOperand(0)->getType() == DestTy) {
+      uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
+      uint32_t DestBitSize = DestTy->getScalarSizeInBits();
+      
+      // We need to emit a shl + ashr to do the sign extend.
+      Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
+      Value *Res = Builder->CreateShl(TI->getOperand(0), ShAmt, "sext");
+      return BinaryOperator::CreateAShr(Res, ShAmt);
+    }
+  
   // If the input is a shl/ashr pair of a same constant, then this is a sign
   // extension from a smaller value.  If we could trust arbitrary bitwidth
   // integers, we could turn this into a truncate to the smaller bit and then
diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 6c0ecc9f9358..ae728ddecfda 100644
--- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -366,7 +366,7 @@ Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
   // alloca dead.
   // If the RHS is an alloca with a two uses, the other one being a 
   // llvm.dbg.declare, zapify the store and the declare, making the
-  // alloca dead.  We must do this to prevent declare's from affecting
+  // alloca dead.  We must do this to prevent declares from affecting
   // codegen.
   if (!SI.isVolatile()) {
     if (Ptr->hasOneUse()) {
@@ -408,8 +408,6 @@ Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
     --BBI;
     // Don't count debug info directives, lest they affect codegen,
     // and we skip pointer-to-pointer bitcasts, which are NOPs.
-    // It is necessary for correctness to skip those that feed into a
-    // llvm.dbg.declare, as these are not present when debugging is off.
     if (isa<DbgInfoIntrinsic>(BBI) ||
         (isa<BitCastInst>(BBI) && isa<PointerType>(BBI->getType()))) {
       ScanInsts++;
@@ -475,9 +473,8 @@ Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
 
   
   // If this store is the last instruction in the basic block (possibly
-  // excepting debug info instructions and the pointer bitcasts that feed
-  // into them), and if the block ends with an unconditional branch, try
-  // to move it to the successor block.
+  // excepting debug info instructions), and if the block ends with an
+  // unconditional branch, try to move it to the successor block.
   BBI = &SI; 
   do {
     ++BBI;
diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 6afc0cdf5360..2e26a75b2ad2 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -407,7 +407,7 @@ Instruction *InstCombiner::visitUDiv(BinaryOperator &I) {
     return Common;
 
   if (ConstantInt *C = dyn_cast<ConstantInt>(Op1)) {
-    // X udiv C^2 -> X >> C
+    // X udiv 2^C -> X >> C
     // Check to see if this is an unsigned division with an exact power of 2,
     // if so, convert to a right shift.
     if (C->getValue().isPowerOf2())  // 0 not included in isPowerOf2
diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp
index fe91da1b6af4..321c91d57d2f 100644
--- a/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -404,12 +404,26 @@ Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
   
   if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
     // If the input is a SHL by the same constant (ashr (shl X, C), C), then we
-    // have a sign-extend idiom.  If the input value is known to already be sign
-    // extended enough, delete the extension.
+    // have a sign-extend idiom.
     Value *X;
-    if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1))) &&
-        ComputeNumSignBits(X) > Op1C->getZExtValue())
-      return ReplaceInstUsesWith(I, X);
+    if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) {
+      // If the input value is known to already be sign extended enough, delete
+      // the extension.
+      if (ComputeNumSignBits(X) > Op1C->getZExtValue())
+        return ReplaceInstUsesWith(I, X);
+
+      // If the input is an extension from the shifted amount value, e.g.
+      //   %x = zext i8 %A to i32
+      //   %y = shl i32 %x, 24
+      //   %z = ashr %y, 24
+      // then turn this into "z = sext i8 A to i32".
+      if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) {
+        uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits();
+        uint32_t DestBits = ZI->getType()->getScalarSizeInBits();
+        if (Op1C->getZExtValue() == DestBits-SrcBits)
+          return new SExtInst(ZI->getOperand(0), ZI->getType());
+      }
+    }
   }            
   
   // See if we can turn a signed shr into an unsigned shr.
diff --git a/lib/Transforms/InstCombine/Makefile b/lib/Transforms/InstCombine/Makefile
index 0c488e78b6d9..f9de42afb0c0 100644
--- a/lib/Transforms/InstCombine/Makefile
+++ b/lib/Transforms/InstCombine/Makefile
@@ -10,6 +10,7 @@
 LEVEL = ../../..
 LIBRARYNAME = LLVMInstCombine
 BUILD_ARCHIVE = 1
+CXXFLAGS = -fno-rtti
 
 include $(LEVEL)/Makefile.common