[vm/compiler] Cleanup unused handling of stack slot locations in comparisons

Location summary for inputs of integer comparisons uses either
RequiresRegister or LocationRegisterOrConstant, so operand cannot be a
StackSlot.

TEST=ci

Change-Id: Idff0f09074be2055f0f9a46d8629c769155eb8ab
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/393044
Reviewed-by: Slava Egorov <[email protected]>
Auto-Submit: Alexander Markov <[email protected]>
Commit-Queue: Slava Egorov <[email protected]>

Author: alexmarkov

runtime/vm/compiler/backend/il_ia32.cc

@@ -766,8 +766,6 @@ static Condition EmitSmiComparisonOp(FlowGraphCompiler* compiler,
     true_condition = FlipCondition(true_condition);
   } else if (right.IsConstant()) {
     __ CompareObject(left.reg(), right.constant());
-  } else if (right.IsStackSlot()) {
-    __ cmpl(left.reg(), LocationToStackSlotAddress(right));
   } else {
     __ cmpl(left.reg(), right.reg());
   }
@@ -793,8 +791,6 @@ static Condition EmitWordComparisonOp(FlowGraphCompiler* compiler,
     __ CompareImmediate(
         left.reg(),
         static_cast<uword>(Integer::Cast(right.constant()).Value()));
-  } else if (right.IsStackSlot()) {
-    __ cmpl(left.reg(), LocationToStackSlotAddress(right));
   } else {
     __ cmpl(left.reg(), right.reg());
   }

runtime/vm/compiler/backend/il_x64.cc

@@ -972,8 +972,6 @@ static Condition EmitSmiComparisonOp(FlowGraphCompiler* compiler,
       ASSERT(constant->representation() == kTagged);
       __ CompareObject(left.reg(), right.constant());
     }
-  } else if (right.IsStackSlot()) {
-    __ OBJ(cmp)(left.reg(), LocationToStackSlotAddress(right));
   } else {
     __ OBJ(cmp)(left.reg(), right.reg());
   }
@@ -1009,8 +1007,6 @@ static Condition EmitInt64ComparisonOp(FlowGraphCompiler* compiler,
     } else {
       UNREACHABLE();
     }
-  } else if (right.IsStackSlot()) {
-    __ cmpq(left.reg(), LocationToStackSlotAddress(right));
   } else {
     __ cmpq(left.reg(), right.reg());
   }