[turbofan] Remove --turbo-loop-stackcheck flag.

The flag in question was on by defautl for a while now and has never
been supported for optimized code generated from bytecode. We no longer
support eliding stack-checks within loops just in optimized code.

R=bmeurer@chromium.org
BUG=v8:5653

Review-Url: https://codereview.chromium.org/2643773008
Cr-Commit-Position: refs/heads/master@{#42574}

src/compiler/ast-graph-builder.cc

@@ -2228,10 +2228,8 @@ void AstGraphBuilder::VisitIterationBody(IterationStatement* stmt,
                                          LoopBuilder* loop,
                                          BailoutId stack_check_id) {
   ControlScopeForIteration scope(this, stmt, loop);
-  if (FLAG_turbo_loop_stackcheck || !info()->shared_info()->asm_function()) {
-    Node* node = NewNode(javascript()->StackCheck());
-    PrepareFrameState(node, stack_check_id);
-  }
+  Node* node = NewNode(javascript()->StackCheck());
+  PrepareFrameState(node, stack_check_id);
   Visit(stmt->body());
 }
 

src/flag-definitions.h

@@ -434,7 +434,6 @@ DEFINE_BOOL(turbo_sp_frame_access, false,
             "use stack pointer-relative access to frame wherever possible")
 DEFINE_BOOL(turbo_preprocess_ranges, true,
             "run pre-register allocation heuristics")
-DEFINE_BOOL(turbo_loop_stackcheck, true, "enable stack checks in loops")
 DEFINE_STRING(turbo_filter, "~~", "optimization filter for TurboFan compiler")
 DEFINE_BOOL(trace_turbo, false, "trace generated TurboFan IR")
 DEFINE_BOOL(trace_turbo_graph, false, "trace generated TurboFan graphs")