[asmjs] Do constant folding for I32Asmjs(Div|Rem)S to avoid checks of constant divisors

src/compiler/wasm-compiler.cc

 // 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.
 
 #include "src/compiler/wasm-compiler.h"
 
 #include <memory>
 
 #include "src/isolate-inl.h"
 
@@ skipping 1849 matching lines @@
 Node* WasmGraphBuilder::BuildI32RemU(Node* left, Node* right,
                                      wasm::WasmCodePosition position) {
   MachineOperatorBuilder* m = jsgraph()->machine();
   return graph()->NewNode(
       m->Uint32Mod(), left, right,
       trap_->ZeroCheck32(wasm::kTrapRemByZero, right, position));
 }
 
 Node* WasmGraphBuilder::BuildI32AsmjsDivS(Node* left, Node* right) {
   MachineOperatorBuilder* m = jsgraph()->machine();
+
+  Int32Matcher mr(right);
+  if (mr.HasValue()) {
+    if (mr.Value() == 0) {
+      return jsgraph()->Int32Constant(0);
+    } else if (mr.Value() == -1) {
+      // The result is the negation of the left input.
+      return graph()->NewNode(m->Int32Sub(), jsgraph()->Int32Constant(0), left);
+    }
+    return graph()->NewNode(m->Int32Div(), left, right, *control_);
+  }
+
   // asm.js semantics return 0 on divide or mod by zero.
   if (m->Int32DivIsSafe()) {
     // The hardware instruction does the right thing (e.g. arm).
     return graph()->NewNode(m->Int32Div(), left, right, graph()->start());
   }
 
   // Check denominator for zero.
   Diamond z(
       graph(), jsgraph()->common(),
       graph()->NewNode(m->Word32Equal(), right, jsgraph()->Int32Constant(0)),
       BranchHint::kFalse);
 
   // Check numerator for -1. (avoid minint / -1 case).
   Diamond n(
       graph(), jsgraph()->common(),
       graph()->NewNode(m->Word32Equal(), right, jsgraph()->Int32Constant(-1)),
       BranchHint::kFalse);
 
   Node* div = graph()->NewNode(m->Int32Div(), left, right, z.if_false);
   Node* neg =
       graph()->NewNode(m->Int32Sub(), jsgraph()->Int32Constant(0), left);
 
   return n.Phi(
       MachineRepresentation::kWord32, neg,
       z.Phi(MachineRepresentation::kWord32, jsgraph()->Int32Constant(0), div));
 }
 
 Node* WasmGraphBuilder::BuildI32AsmjsRemS(Node* left, Node* right) {
   MachineOperatorBuilder* m = jsgraph()->machine();
+
+  Int32Matcher mr(right);
+  if (mr.HasValue()) {
+    if (mr.Value() == 0) {
+      return jsgraph()->Int32Constant(0);
+    } else if (mr.Value() == -1) {
+      return jsgraph()->Int32Constant(0);
+    }
+    return graph()->NewNode(m->Int32Mod(), left, right, *control_);
+  }
+
   // asm.js semantics return 0 on divide or mod by zero.
   // Explicit check for x % 0.
   Diamond z(
       graph(), jsgraph()->common(),
       graph()->NewNode(m->Word32Equal(), right, jsgraph()->Int32Constant(0)),
       BranchHint::kFalse);
 
   // Explicit check for x % -1.
   Diamond d(
       graph(), jsgraph()->common(),
@@ skipping 1550 matching lines @@
                             function_->code_start_offset),
            compile_ms);
   }
 
   return code;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8