[InstCombine] refactor optimizeIntToFloatBitCast() ; NFCI

The logic for handling the pattern without a shift is identical
to the logic for handling the pattern with a shift if you set 
the shift amount to zero for the former.

This should make it easier to see that we probably don't even need
optimizeIntToFloatBitCast(). 

If we call something like foldVecTruncToExtElt() from visitTrunc(),
we'll solve PR25543:
https://llvm.org/bugs/show_bug.cgi?id=25543

llvm-svn: 253403

1 files changed, 29 insertions, 38 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 3cf8561a1d3..18415efb16f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1715,62 +1715,53 @@ static Value *optimizeIntegerToVectorInsertions(BitCastInst &CI,
   return Result;
 }
 
+static Instruction *foldVecTruncToExtElt(Value *VecInput, Type *DestTy,
+                                         unsigned ShiftAmt, InstCombiner &IC,
+                                         const DataLayout &DL) {
+  VectorType *VecTy = cast<VectorType>(VecInput->getType());
+  unsigned DestWidth = DestTy->getPrimitiveSizeInBits();
+  unsigned VecWidth = VecTy->getPrimitiveSizeInBits();
+
+  if ((VecWidth % DestWidth != 0) || (ShiftAmt % DestWidth != 0))
+    return nullptr;
+
+  // If the element type of the vector doesn't match the result type,
+  // bitcast it to be a vector type we can extract from.
+  unsigned NumVecElts = VecWidth / DestWidth;
+  if (VecTy->getElementType() != DestTy) {
+    VecTy = VectorType::get(DestTy, NumVecElts);
+    VecInput = IC.Builder->CreateBitCast(VecInput, VecTy);
+  }
+
+  unsigned Elt = ShiftAmt / DestWidth;
+  if (DL.isBigEndian())
+    Elt = NumVecElts - 1 - Elt;
+
+  return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(Elt));
+}
 
 /// 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,
                                               const DataLayout &DL) {
   Value *Src = CI.getOperand(0);
-  Type *DestTy = CI.getType();
+  Type *DstTy = CI.getType();
 
   // If this is a bitcast from int to float, check to see if the int is an
   // extraction from a vector.
   Value *VecInput = nullptr;
   // bitcast(trunc(bitcast(somevector)))
   if (match(Src, m_Trunc(m_BitCast(m_Value(VecInput)))) &&
-      isa<VectorType>(VecInput->getType())) {
-    VectorType *VecTy = cast<VectorType>(VecInput->getType());
-    unsigned DestWidth = DestTy->getPrimitiveSizeInBits();
-
-    if (VecTy->getPrimitiveSizeInBits() % DestWidth == 0) {
-      // If the element type of the vector doesn't match the result type,
-      // bitcast it to be a vector type we can extract from.
-      if (VecTy->getElementType() != DestTy) {
-        VecTy = VectorType::get(DestTy,
-                                VecTy->getPrimitiveSizeInBits() / DestWidth);
-        VecInput = IC.Builder->CreateBitCast(VecInput, VecTy);
-      }
-
-      unsigned Elt = 0;
-      if (DL.isBigEndian())
-        Elt = VecTy->getPrimitiveSizeInBits() / DestWidth - 1;
-      return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(Elt));
-    }
-  }
+      isa<VectorType>(VecInput->getType()))
+    return foldVecTruncToExtElt(VecInput, DstTy, 0, IC, DL);
 
   // bitcast(trunc(lshr(bitcast(somevector), cst))
   ConstantInt *ShAmt = nullptr;
   if (match(Src, m_Trunc(m_LShr(m_BitCast(m_Value(VecInput)),
                                 m_ConstantInt(ShAmt)))) &&
-      isa<VectorType>(VecInput->getType())) {
-    VectorType *VecTy = cast<VectorType>(VecInput->getType());
-    unsigned DestWidth = DestTy->getPrimitiveSizeInBits();
-    if (VecTy->getPrimitiveSizeInBits() % DestWidth == 0 &&
-        ShAmt->getZExtValue() % DestWidth == 0) {
-      // If the element type of the vector doesn't match the result type,
-      // bitcast it to be a vector type we can extract from.
-      if (VecTy->getElementType() != DestTy) {
-        VecTy = VectorType::get(DestTy,
-                                VecTy->getPrimitiveSizeInBits() / DestWidth);
-        VecInput = IC.Builder->CreateBitCast(VecInput, VecTy);
-      }
+      isa<VectorType>(VecInput->getType()))
+    return foldVecTruncToExtElt(VecInput, DstTy, ShAmt->getZExtValue(), IC, DL);
 
-      unsigned Elt = ShAmt->getZExtValue() / DestWidth;
-      if (DL.isBigEndian())
-        Elt = VecTy->getPrimitiveSizeInBits() / DestWidth - 1 - Elt;
-      return ExtractElementInst::Create(VecInput, IC.Builder->getInt32(Elt));
-    }
-  }
   return nullptr;
 }