[InstCombine] Remove deadcode in `(icmp SignTest(shl/shr X))`; NFC

[goldstein.w.n]

Summary

This is dead as of: D145341

[goldstein.w.n]

Actual commit

[nikic]

LG

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

if (Pred == ICmpInst::ICMP_SLT) {
       // SLE is the same as above, but SLE is canonicalized to SLT, so convert:
       // (X << S) <=s C is equiv to X <=s (C >> S) for all C
       // (X << S) <s (C + 1) is equiv to X <s (C >> S) + 1 if C <s SMAX
       // (X << S) <s C is equiv to X <s ((C - 1) >> S) + 1 if C >s SMIN
       assert(!C.isMinSignedValue() && "Unexpected icmp slt");
       APInt ShiftedC = (C - 1).ashr(*ShiftAmt) + 1;
       return new ICmpInst(Pred, X, ConstantInt::get(ShType, ShiftedC));
     }
-    // If this is a signed comparison to 0 and the shift is sign preserving,
-    // use the shift LHS operand instead; isSignTest may change 'Pred', so only
-    // do that if we're sure to not continue on in this function.
-    if (isSignTest(Pred, C))
-      return new ICmpInst(Pred, X, Constant::getNullValue(ShType));
   }
 
   // NUW guarantees that we are only shifting out zero bits from the high bits,
   // so we can LSHR the compare constant without needing a mask and eliminate
   // the shift.
   if (Shl->hasNoUnsignedWrap()) {
     if (Pred == ICmpInst::ICMP_UGT) {
       // icmp Pred (shl nuw X, ShiftAmt), C --> icmp Pred X, (C >>u ShiftAmt)