[arm64] Emit CBZ for deoptimisations.

Emit the compare and branch on zero (CBZ) instruction when
possible for deoptimisations, as we do for normal branches.

BUG=

Review-Url: https://codereview.chromium.org/2448113002
Cr-Commit-Position: refs/heads/master@{#40568}

src/compiler/arm64/instruction-selector-arm64.cc

@@ -2152,6 +2152,20 @@ FlagsCondition MapForCbz(FlagsCondition cond) {
   }
 }
 
+void EmitBranchOrDeoptimize(InstructionSelector* selector,
+                            InstructionCode opcode, InstructionOperand value,
+                            FlagsContinuation* cont) {
+  Arm64OperandGenerator g(selector);
+  if (cont->IsBranch()) {
+    selector->Emit(cont->Encode(opcode), g.NoOutput(), value,
+                   g.Label(cont->true_block()), g.Label(cont->false_block()));
+  } else {
+    DCHECK(cont->IsDeoptimize());
+    selector->EmitDeoptimize(cont->Encode(opcode), g.NoOutput(), value,
+                             cont->reason(), cont->frame_state());
+  }
+}
+
 // Try to emit TBZ, TBNZ, CBZ or CBNZ for certain comparisons of {node}
 // against zero, depending on the condition.
 bool TryEmitCbzOrTbz(InstructionSelector* selector, Node* node, Node* user,
@@ -2160,12 +2174,16 @@ bool TryEmitCbzOrTbz(InstructionSelector* selector, Node* node, Node* user,
   USE(m_user);
   DCHECK(m_user.right().Is(0) || m_user.left().Is(0));
 
-  // Only handle branches.
-  if (!cont->IsBranch()) return false;
+  // Only handle branches and deoptimisations.
+  if (!cont->IsBranch() && !cont->IsDeoptimize()) return false;
 
   switch (cond) {
     case kSignedLessThan:
     case kSignedGreaterThanOrEqual: {
+      // We don't generate TBZ/TBNZ for deoptimisations, as they have a
+      // shorter range than conditional branches and generating them for
+      // deoptimisations results in more veneers.
+      if (cont->IsDeoptimize()) return false;
       Arm64OperandGenerator g(selector);
       cont->Overwrite(MapForTbz(cond));
       Int32Matcher m(node);
@@ -2192,9 +2210,8 @@ bool TryEmitCbzOrTbz(InstructionSelector* selector, Node* node, Node* user,
     case kUnsignedGreaterThan: {
       Arm64OperandGenerator g(selector);
       cont->Overwrite(MapForCbz(cond));
-      selector->Emit(cont->Encode(kArm64CompareAndBranch32), g.NoOutput(),
-                     g.UseRegister(node), g.Label(cont->true_block()),
-                     g.Label(cont->false_block()));
+      EmitBranchOrDeoptimize(selector, kArm64CompareAndBranch32,
+                             g.UseRegister(node), cont);
       return true;
     }
     default:
@@ -2380,10 +2397,10 @@ void VisitWordCompareZero(InstructionSelector* selector, Node* user,
                                     kLogical64Imm);
           }
           // Merge the Word64Equal(x, 0) comparison into a cbz instruction.
-          if (cont->IsBranch()) {
-            selector->Emit(cont->Encode(kArm64CompareAndBranch), g.NoOutput(),
-                           g.UseRegister(left), g.Label(cont->true_block()),
-                           g.Label(cont->false_block()));
+          if (cont->IsBranch() || cont->IsDeoptimize()) {
+            EmitBranchOrDeoptimize(selector,
+                                   cont->Encode(kArm64CompareAndBranch),
+                                   g.UseRegister(left), cont);
             return;
           }
         }

src/compiler/instruction-selector.cc

@@ -2017,6 +2017,18 @@ void InstructionSelector::VisitReturn(Node* ret) {
   }
 }
 
+Instruction* InstructionSelector::EmitDeoptimize(InstructionCode opcode,
+                                                 InstructionOperand output,
+                                                 InstructionOperand a,
+                                                 DeoptimizeReason reason,
+                                                 Node* frame_state) {
+  size_t output_count = output.IsInvalid() ? 0 : 1;
+  InstructionOperand inputs[] = {a};
+  size_t input_count = arraysize(inputs);
+  return EmitDeoptimize(opcode, output_count, &output, input_count, inputs,
+                        reason, frame_state);
+}
+
 Instruction* InstructionSelector::EmitDeoptimize(
     InstructionCode opcode, InstructionOperand output, InstructionOperand a,
     InstructionOperand b, DeoptimizeReason reason, Node* frame_state) {

src/compiler/instruction-selector.h

@@ -110,6 +110,9 @@ class V8_EXPORT_PRIVATE InstructionSelector final {
   // ===== Architecture-independent deoptimization exit emission methods. ======
   // ===========================================================================
 
+  Instruction* EmitDeoptimize(InstructionCode opcode, InstructionOperand output,
+                              InstructionOperand a, DeoptimizeReason reason,
+                              Node* frame_state);
   Instruction* EmitDeoptimize(InstructionCode opcode, InstructionOperand output,
                               InstructionOperand a, InstructionOperand b,
                               DeoptimizeReason reason, Node* frame_state);