[X86] Remove ANY_EXTEND special case from canReduceVMulWidth

[craig.topper]

Summary

Removing this code doesn't affect any lit tests so it doesn't appear to be tested anymore. I assume it was when it was added, but I guess something else changed?

I mostly didn't like that it seemed to count the sign bits as if it was a sign_extend, but then set isPositive as if it was a zero_extend. It feels like we should have picked one interpretation?

[RKSimon]

LGTM - code coverage report says its unused as well

llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

if (VT.getScalarSizeInBits() != 32)
     return false;
 
   assert(N->getNumOperands() == 2 && "NumOperands of Mul are 2");
   unsigned SignBits[2] = {1, 1};
   bool IsPositive[2] = {false, false};
   for (unsigned i = 0; i < 2; i++) {
     SDValue Opd = N->getOperand(i);
 
-    // DAG.ComputeNumSignBits return 1 for ISD::ANY_EXTEND, so we need to
-    // compute signbits for it separately.
-    if (Opd.getOpcode() == ISD::ANY_EXTEND) {
-      // For anyextend, it is safe to assume an appropriate number of leading
-      // sign/zero bits.
-      if (Opd.getOperand(0).getValueType().getVectorElementType() == MVT::i8)
-        SignBits[i] = 25;
-      else if (Opd.getOperand(0).getValueType().getVectorElementType() ==
-               MVT::i16)
-        SignBits[i] = 17;
-      else
-        return false;
-      IsPositive[i] = true;
-    } else {
-      SignBits[i] = DAG.ComputeNumSignBits(Opd);
-      if (DAG.SignBitIsZero(Opd))
-        IsPositive[i] = true;
-    }
+    IsPositive[i] = DAG.SignBitIsZero(Opd);
   }
 
   bool AllPositive = IsPositive[0] && IsPositive[1];
   unsigned MinSignBits = std::min(SignBits[0], SignBits[1]);
   // When ranges are from -128 ~ 127, use MULS8 mode.
   if (MinSignBits >= 25)
     Mode = MULS8;
   // When ranges are from 0 ~ 255, use MULU8 mode.