1 files changed, 57 insertions, 22 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 0390368c4bb..078a80de2df 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -18,6 +18,7 @@
 #include "llvm/IR/DIBuilder.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/Support/KnownBits.h"
+#include <numeric>
 using namespace llvm;
 using namespace PatternMatch;
 
@@ -1820,12 +1821,24 @@ Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) {
 }
 
 /// This input value (which is known to have vector type) is being zero extended
-/// or truncated to the specified vector type.
+/// or truncated to the specified vector type. Since the zext/trunc is done
+/// using an integer type, we have a (bitcast(cast(bitcast))) pattern,
+/// endianness will impact which end of the vector that is extended or
+/// truncated.
+///
+/// A vector is always stored with index 0 at the lowest address, which
+/// corresponds to the most significant bits for a big endian stored integer and
+/// the least significant bits for little endian. A trunc/zext of an integer
+/// impacts the big end of the integer. Thus, we need to add/remove elements at
+/// the front of the vector for big endian targets, and the back of the vector
+/// for little endian targets.
+///
 /// Try to replace it with a shuffle (and vector/vector bitcast) if possible.
 ///
 /// The source and destination vector types may have different element types.
-static Instruction *optimizeVectorResize(Value *InVal, VectorType *DestTy,
-                                         InstCombiner &IC) {
+static Instruction *optimizeVectorResizeWithIntegerBitCasts(Value *InVal,
+                                                            VectorType *DestTy,
+                                                            InstCombiner &IC) {
   // We can only do this optimization if the output is a multiple of the input
   // element size, or the input is a multiple of the output element size.
   // Convert the input type to have the same element type as the output.
@@ -1844,31 +1857,53 @@ static Instruction *optimizeVectorResize(Value *InVal, VectorType *DestTy,
     InVal = IC.Builder.CreateBitCast(InVal, SrcTy);
   }
 
+  bool IsBigEndian = IC.getDataLayout().isBigEndian();
+  unsigned SrcElts = SrcTy->getNumElements();
+  unsigned DestElts = DestTy->getNumElements();
+
+  assert(SrcElts != DestElts && "Element counts should be different.");
+
   // Now that the element types match, get the shuffle mask and RHS of the
   // shuffle to use, which depends on whether we're increasing or decreasing the
   // size of the input.
-  SmallVector<uint32_t, 16> ShuffleMask;
+  SmallVector<uint32_t, 16> ShuffleMaskStorage;
+  ArrayRef<uint32_t> ShuffleMask;
   Value *V2;
 
-  if (SrcTy->getNumElements() > DestTy->getNumElements()) {
-    // If we're shrinking the number of elements, just shuffle in the low
-    // elements from the input and use undef as the second shuffle input.
-    V2 = UndefValue::get(SrcTy);
-    for (unsigned i = 0, e = DestTy->getNumElements(); i != e; ++i)
-      ShuffleMask.push_back(i);
+  // Produce an identify shuffle mask for the src vector.
+  ShuffleMaskStorage.resize(SrcElts);
+  std::iota(ShuffleMaskStorage.begin(), ShuffleMaskStorage.end(), 0);
 
+  if (SrcElts > DestElts) {
+    // If we're shrinking the number of elements (rewriting an integer
+    // truncate), just shuffle in the elements corresponding to the least
+    // significant bits from the input and use undef as the second shuffle
+    // input.
+    V2 = UndefValue::get(SrcTy);
+    // Make sure the shuffle mask selects the "least significant bits" by
+    // keeping elements from back of the src vector for big endian, and from the
+    // front for little endian.
+    ShuffleMask = ShuffleMaskStorage;
+    if (IsBigEndian)
+      ShuffleMask = ShuffleMask.take_back(DestElts);
+    else
+      ShuffleMask = ShuffleMask.take_front(DestElts);
   } else {
-    // If we're increasing the number of elements, shuffle in all of the
-    // elements from InVal and fill the rest of the result elements with zeros
-    // from a constant zero.
+    // If we're increasing the number of elements (rewriting an integer zext),
+    // shuffle in all of the elements from InVal. Fill the rest of the result
+    // elements with zeros from a constant zero.
     V2 = Constant::getNullValue(SrcTy);
-    unsigned SrcElts = SrcTy->getNumElements();
-    for (unsigned i = 0, e = SrcElts; i != e; ++i)
-      ShuffleMask.push_back(i);
-
-    // The excess elements reference the first element of the zero input.
-    for (unsigned i = 0, e = DestTy->getNumElements()-SrcElts; i != e; ++i)
-      ShuffleMask.push_back(SrcElts);
+    // Use first elt from V2 when indicating zero in the shuffle mask.
+    uint32_t NullElt = SrcElts;
+    // Extend with null values in the "most significant bits" by adding elements
+    // in front of the src vector for big endian, and at the back for little
+    // endian.
+    unsigned DeltaElts = DestElts - SrcElts;
+    if (IsBigEndian)
+      ShuffleMaskStorage.insert(ShuffleMaskStorage.begin(), DeltaElts, NullElt);
+    else
+      ShuffleMaskStorage.append(DeltaElts, NullElt);
+    ShuffleMask = ShuffleMaskStorage;
   }
 
   return new ShuffleVectorInst(InVal, V2,
@@ -2375,8 +2410,8 @@ Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
         CastInst *SrcCast = cast<CastInst>(Src);
         if (BitCastInst *BCIn = dyn_cast<BitCastInst>(SrcCast->getOperand(0)))
           if (isa<VectorType>(BCIn->getOperand(0)->getType()))
-            if (Instruction *I = optimizeVectorResize(BCIn->getOperand(0),
-                                               cast<VectorType>(DestTy), *this))
+            if (Instruction *I = optimizeVectorResizeWithIntegerBitCasts(
+                    BCIn->getOperand(0), cast<VectorType>(DestTy), *this))
               return I;
       }