Make InstCombineCasts.cpp:OptimizeIntToFloatBitCast endian safe.

The OptimizeIntToFloatBitCast converts shift-truncate sequences
into extractelement operations.  The computation of the element
index to be used in the resulting operation is currently only
correct for little-endian targets.

This commit fixes the element index computation to be correct
for big-endian targets as well.  If the target byte order is
unknown, the optimization cannot be performed at all.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178031 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -1610,6 +1610,9 @@ static Value *OptimizeIntegerToVectorInsertions(BitCastInst &CI,
 /// OptimizeIntToFloatBitCast - See if we can optimize an integer->float/double
 /// bitcast.  The various long double bitcasts can't get in here.
 static Instruction *OptimizeIntToFloatBitCast(BitCastInst &CI,InstCombiner &IC){
+  // We need to know the target byte order to perform this optimization.
+  if (!IC.getDataLayout()) return 0;
+
   Value *Src = CI.getOperand(0);
   Type *DestTy = CI.getType();
 
@@ -1631,7 +1634,10 @@ static Instruction *OptimizeIntToFloatBitCast(BitCastInst &CI,InstCombiner &IC){
         VecInput = IC.Builder->CreateBitCast(VecInput, VecTy);
       }
 
-      return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(0));
+      unsigned Elt = 0;
+      if (IC.getDataLayout()->isBigEndian())
+        Elt = VecTy->getPrimitiveSizeInBits() / DestWidth - 1;
+      return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(Elt));
     }
   }
 
@@ -1653,6 +1659,8 @@ static Instruction *OptimizeIntToFloatBitCast(BitCastInst &CI,InstCombiner &IC){
       }
 
       unsigned Elt = ShAmt->getZExtValue() / DestWidth;
+      if (IC.getDataLayout()->isBigEndian())
+        Elt = VecTy->getPrimitiveSizeInBits() / DestWidth - 1 - Elt;
       return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(Elt));
     }
   }