[llvm] r346995 - [X86] Remove ANY_EXTEND special case from canReduceVMulWidth

[Craig Topper via llvm-commits]

Author: ctopper
Date: Thu Nov 15 13:19:32 2018
New Revision: 346995

URL: http://llvm.org/viewvc/llvm-project?rev=346995&view=rev
Log:
[X86] Remove ANY_EXTEND special case from canReduceVMulWidth

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? Code coverage report also says its unused.

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?

Differential Revision: https://reviews.llvm.org/D54596

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

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=346995&r1=346994&r2=346995&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Thu Nov 15 13:19:32 2018
@@ -34337,24 +34337,8 @@ static bool canReduceVMulWidth(SDNode *N
   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;
-    }
+    SignBits[i] = DAG.ComputeNumSignBits(Opd);
+    IsPositive[i] = DAG.SignBitIsZero(Opd);
   }
 
   bool AllPositive = IsPositive[0] && IsPositive[1];