Revert of [turbofan] Better representation selection for comparison w…

…ith Float64. (patchset crosswalk-project#2 id:20001 of https://codereview.chromium.org/2790833004/ )

Reason for revert:
Doesn't really move the needle, but tanks Kraken/imaging-gaussian-blur (crbug.com/709396), so reverting for now.

Original issue's description:
> [turbofan] Better representation selection for comparison with Float64.
>
> For speculative number comparisons with SignedSmall feedback, we always
> enforce either TaggedSigned or Word32 comparisons. But this is not
> really beneficial if one of the inputs is already in Float64
> representation; in that case it's cheaper to just convert the other
> input to a Float64.
>
> [email protected]
>
> Review-Url: https://codereview.chromium.org/2790833004
> Cr-Commit-Position: refs/heads/master@{#44327}
> Committed: https://chromium.googlesource.com/v8/v8/+/8af394d6d385daf05b73765a2545ac8f266c64c7

[email protected]
BUG=chromium:709396

Review-Url: https://codereview.chromium.org/2801233002
Cr-Commit-Position: refs/heads/master@{#44480}

src/compiler/simplified-lowering.cc

@@ -701,11 +701,6 @@ class RepresentationSelector {
            GetUpperBound(node->InputAt(1))->Is(type);
   }
 
-  bool IsNodeRepresentationFloat64(Node* node) {
-    MachineRepresentation representation = GetInfo(node)->representation();
-    return representation == MachineRepresentation::kFloat64;
-  }
-
   bool IsNodeRepresentationTagged(Node* node) {
     MachineRepresentation representation = GetInfo(node)->representation();
     return IsAnyTagged(representation);
@@ -1624,15 +1619,6 @@ class RepresentationSelector {
                 ChangeToPureOp(
                     node, changer_->TaggedSignedOperatorFor(node->opcode()));
 
-              } else if (IsNodeRepresentationFloat64(lhs) ||
-                         IsNodeRepresentationFloat64(rhs)) {
-                // If one side is already a Float64, it's pretty expensive to
-                // do the comparison in Word32, since that means we need a
-                // checked conversion from Float64 to Word32. It's cheaper to
-                // just go to Float64 for the comparison.
-                VisitBinop(node, UseInfo::CheckedNumberAsFloat64(),
-                           MachineRepresentation::kBit);
-                ChangeToPureOp(node, Float64Op(node));
               } else {
                 VisitBinop(node, CheckedUseInfoAsWord32FromHint(hint),
                            MachineRepresentation::kBit);