[wasm] Introduce the TrapIf and TrapUnless operators to generate trap code.

src/compiler/wasm-compiler.cc

Index: src/compiler/wasm-compiler.cc
diff --git a/src/compiler/wasm-compiler.cc b/src/compiler/wasm-compiler.cc
index b0e76e6b2daf6d2efa4d67ea5680e88edd7d404e..f114db47af496df222e8b63869556a7f767d5fd7 100644
--- a/src/compiler/wasm-compiler.cc
+++ b/src/compiler/wasm-compiler.cc
@@ -168,15 +168,50 @@ class WasmTrapHelper : public ZoneObject {
     return TrapIfEq64(reason, node, 0, position);
   }
 
+  int32_t GetFunctionIdForTrap(wasm::TrapReason reason) {
+    int32_t trap_id;
+    if (builder_->module_ && !builder_->module_->instance->context.is_null()) {
+      trap_id = wasm::WasmOpcodes::TrapReasonToFunctionId(reason);
+    } else {
+      // We use Runtime::kNumFunctions as a marker to tell the code generator
+      // to generate a call to a testing c-function instead of a runtime
+      // function. This code should only be called from a cctest.
+      trap_id = Runtime::kNumFunctions;
+    }
+    return trap_id;
+  }
+
   // Add a trap if {cond} is true.
   void AddTrapIfTrue(wasm::TrapReason reason, Node* cond,
                      wasm::WasmCodePosition position) {
+#if V8_TARGET_ARCH_X64

[titzer, 2016/12/12 14:21:33]

Can you introduce another preprocessor definition, like WASM_TRAP_IF_SUPPORTED,
so that we can just change that macro as each new platform gets added (and
eventually remove)?

[ahaas, 2016/12/13 12:38:59]

Done.

+    if (FLAG_wasm_trap_if) {
+      int32_t trap_id = GetFunctionIdForTrap(reason);
+      Node* node = graph()->NewNode(common()->TrapIf(trap_id), cond,
+                                    builder_->Effect(), builder_->Control());
+      *builder_->control_ = node;
+      builder_->SetSourcePosition(node, position);
+      return;
+    }
+#endif  // V8_TARGET_ARCH_X64
     AddTrapIf(reason, cond, true, position);

[titzer, 2016/12/12 14:21:33]

Can we rename this internal function to BuildTrapIf() since they build an actual
subgraph as opposed to using the special TrapIf operator?

[ahaas, 2016/12/13 12:38:59]

Done.

   }
 
   // Add a trap if {cond} is false.
   void AddTrapIfFalse(wasm::TrapReason reason, Node* cond,
                       wasm::WasmCodePosition position) {
+#if V8_TARGET_ARCH_X64
+    if (FLAG_wasm_trap_if) {
+      int32_t trap_id = GetFunctionIdForTrap(reason);
+
+      Node* node = graph()->NewNode(common()->TrapUnless(trap_id), cond,
+                                    builder_->Effect(), builder_->Control());
+      *builder_->control_ = node;
+      builder_->SetSourcePosition(node, position);
+      return;
+    }
+#endif  // V8_TARGET_ARCH_X64
+
     AddTrapIf(reason, cond, false, position);
   }