Revert "[vm/compiler] Optimize switch statements"

This reverts commit f522812.

Reason for revert: causes a VM crash, see b/242964932 (the test is also publicly available at https://github.com/simolus3/drift/blob/93fb0da38a5f33c8db289bfde696b0ca3d401b7f/drift_dev/test/analyzer/sql_queries/query_analyzer_test.dart#L8)

Original change's description:
> [vm/compiler] Optimize switch statements
>
> Switch statements that either contain only integers or only enum values of the same type can be optimized.
>
> Depending on the number of switch expressions and the number of holes that the range of switch expressions contains, either a binary search or a jump table is used.
>
> TEST=runtime/test/vm/dart{,_2}/optimized_switch
> TEST=tests/language{,_2}/switch
>
> Fixes: #49585
>
> Co-authored-by: Gabriel Terwesten [email protected]
>
> Change-Id: I62dcdb7843107f03de7e468c60b4db52ec78f676
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/253787
> Reviewed-by: Alexander Markov <[email protected]>
> Commit-Queue: Alexander Markov <[email protected]>

[email protected],[email protected],[email protected]

Change-Id: I8c673ea70e7ed91dffb3674e7dcb4aaa0611e978
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/255258
Reviewed-by: Slava Egorov <[email protected]>
Reviewed-by: Ilya Yanok <[email protected]>
Commit-Queue: Slava Egorov <[email protected]>

Author: Ilya Yanok

runtime/tests/vm/dart/optimized_switch_test.dart

@@ -284,10 +284,8 @@ void IfConverter::Simplify(FlowGraph* flow_graph) {
         BranchInstr* branch = pred->last_instruction()->AsBranch();
 
         if (branch == nullptr) {
-          // There is no "B_pred" block, or the block is the IndirectGoto
-          // of a switch that uses it as a jump table.
-          ASSERT(pred->last_instruction()->IsGraphEntry() ||
-                 pred->last_instruction()->IsIndirectGoto());
+          // There is no "B_pred" block.
+          ASSERT(pred->last_instruction()->IsGraphEntry());
           continue;
         }
 

runtime/tests/vm/dart_2/optimized_switch_test.dart

@@ -232,10 +232,8 @@ void ConstantPropagator::VisitGoto(GotoInstr* instr) {
 }
 
 void ConstantPropagator::VisitIndirectGoto(IndirectGotoInstr* instr) {
-  if (reachable_->Contains(instr->GetBlock()->preorder_number())) {
-    for (intptr_t i = 0; i < instr->SuccessorCount(); i++) {
-      SetReachable(instr->SuccessorAt(i));
-    }
+  for (intptr_t i = 0; i < instr->SuccessorCount(); i++) {
+    SetReachable(instr->SuccessorAt(i));
   }
 }
 
@@ -1504,11 +1502,7 @@ static bool HasPhis(BlockEntryInstr* block) {
 }
 
 static bool IsEmptyBlock(BlockEntryInstr* block) {
-  // A block containing a goto to itself forms an infinite loop.
-  // We don't consider this an empty block to handle the edge-case where code
-  // reduces to an infinite loop.
-  return block->next()->IsGoto() &&
-         block->next()->AsGoto()->successor() != block && !HasPhis(block) &&
+  return block->next()->IsGoto() && !HasPhis(block) &&
          !block->IsIndirectEntry();
 }