handle WASM trap in the instruction scheduler.

src/compiler/instruction-scheduler.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_INSTRUCTION_SCHEDULER_H_
 #define V8_COMPILER_INSTRUCTION_SCHEDULER_H_
 
 #include "src/compiler/instruction.h"
 #include "src/zone/zone-containers.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 // A set of flags describing properties of the instructions so that the
 // scheduler is aware of dependencies between instructions.
 enum ArchOpcodeFlags {
   kNoOpcodeFlags = 0,
   kIsBlockTerminator = 1,  // The instruction marks the end of a basic block
                            // e.g.: jump and return instructions.
   kHasSideEffect = 2,      // The instruction has some side effects (memory
                            // store, function call...)
   kIsLoadOperation = 4,    // The instruction is a memory load.
-  kMayNeedDeoptCheck = 8,  // The instruction might be associated with a deopt
-                           // check. This is the case of instruction which can
-                           // blow up with particular inputs (e.g.: division by
-                           // zero on Intel platforms).
+  kMayNeedDeoptOrTrapCheck = 8,  // The instruction may be associated with a
+                                 // deopt or trap check which must be run before
+                                 // instruction e.g. div on Intel platform which
+                                 // will raise an exception when the divisor is
+                                 // zero.
 };
 
 class InstructionScheduler final : public ZoneObject {
  public:
   InstructionScheduler(Zone* zone, InstructionSequence* sequence);
 
   void StartBlock(RpoNumber rpo);
   void EndBlock(RpoNumber rpo);
 
   void AddInstruction(Instruction* instr);
@@ skipping 121 matching lines @@
   // memory store).
   bool HasSideEffect(const Instruction* instr) const {
     return (GetInstructionFlags(instr) & kHasSideEffect) != 0;
   }
 
   // Return true if the instruction is a memory load.
   bool IsLoadOperation(const Instruction* instr) const {
     return (GetInstructionFlags(instr) & kIsLoadOperation) != 0;
   }
 
-  // Return true if this instruction is usually associated with a deopt check
-  // to validate its input.
-  bool MayNeedDeoptCheck(const Instruction* instr) const {
-    return (GetInstructionFlags(instr) & kMayNeedDeoptCheck) != 0;
+  // The scheduler will not move the following instructions before the last
+  // deopt/trap check:
+  //  * loads (this is conservative)
+  //  * instructions with side effect
+  //  * other deopts/traps
+  // Any other instruction can be moved, apart from those that raise exceptions
+  // on specific inputs - these are filtered out by the deopt/trap check.
+  bool MayNeedDeoptOrTrapCheck(const Instruction* instr) const {
+    return (GetInstructionFlags(instr) & kMayNeedDeoptOrTrapCheck) != 0;
   }
 
-  // Return true if the instruction cannot be moved before the last deopt
-  // point we encountered.
-  bool DependsOnDeoptimization(const Instruction* instr) const {
-    return MayNeedDeoptCheck(instr) || instr->IsDeoptimizeCall() ||
-           HasSideEffect(instr) || IsLoadOperation(instr);
+  // Return true if the instruction cannot be moved before the last deopt or
+  // trap point we encountered.
+  bool DependsOnDeoptOrTrap(const Instruction* instr) const {
+    return MayNeedDeoptOrTrapCheck(instr) || instr->IsDeoptimizeCall() ||
+           instr->IsTrap() || HasSideEffect(instr) || IsLoadOperation(instr);
   }
 
   // Identify nops used as a definition point for live-in registers at
   // function entry.
   bool IsFixedRegisterParameter(const Instruction* instr) const {
     return (instr->arch_opcode() == kArchNop) && (instr->OutputCount() == 1) &&
            (instr->OutputAt(0)->IsUnallocated()) &&
            (UnallocatedOperand::cast(instr->OutputAt(0))
                 ->HasFixedRegisterPolicy() ||
             UnallocatedOperand::cast(instr->OutputAt(0))
@@ skipping 20 matching lines @@
   // effects.
   ZoneVector<ScheduleGraphNode*> pending_loads_;
 
   // Live-in register markers are nop instructions which are emitted at the
   // beginning of a basic block so that the register allocator will find a
   // defining instruction for live-in values. They must not be moved.
   // All these nops are chained together and added as a predecessor of every
   // other instructions in the basic block.
   ScheduleGraphNode* last_live_in_reg_marker_;
 
-  // Last deoptimization instruction encountered while building the graph.
-  ScheduleGraphNode* last_deopt_;
+  // Last deoptimization or trap instruction encountered while building the
+  // graph.
+  ScheduleGraphNode* last_deopt_or_trap_;
 
   // Keep track of definition points for virtual registers. This is used to
   // record operand dependencies in the scheduling graph.
   ZoneMap<int32_t, ScheduleGraphNode*> operands_map_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_SCHEDULER_H_