[wasm] Implemented F32Trunc as a turbofan graph based on int32 instructions.

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 64b3089952d32f6b093d42adb24e28c43b5ccc59..b7f04d42ac9991c1ab5016c90b09572613f10c79 100644
--- a/src/compiler/wasm-compiler.cc
+++ b/src/compiler/wasm-compiler.cc
@@ -756,11 +756,10 @@ Node* WasmGraphBuilder::Unop(wasm::WasmOpcode opcode, Node* input) {
     case wasm::kExprF32Trunc: {
       if (m->Float32RoundTruncate().IsSupported()) {
         op = m->Float32RoundTruncate().op();
-        break;
       } else {
-        op = UnsupportedOpcode(opcode);
-        break;
+        return BuildF32Trunc(input);
       }
+      break;
     }
     case wasm::kExprF32NearestInt: {
       if (m->Float32RoundTiesEven().IsSupported()) {
@@ -1365,6 +1364,73 @@ Node* WasmGraphBuilder::BuildI64Popcnt(Node* input) {
 }
 
 
+Node* WasmGraphBuilder::BuildF32Trunc(Node* input) {
+  //  int32_t int_input = bitftoi(input);
+  //  int32_t exponent = int_input & 0x7f800000;
+  //  if (exponent >= ((23 + 127) << 23)) {
+  //    if (input != input) {
+  //      return bititof(int_input | (1 << 22));
+  //    }
+  //    return input;
+  //  }
+  //  int32_t sign = int_input & 0x80000000;
+  //  if (exponent < (127 << 23)) {
+  //    return bititof(sign);
+  //  }
+  //  int32_t mantissa = int_input & 0x007fffff;
+  //  int32_t shift = (127 + 23) - (exponent >> 23);
+  //  int32_t new_mantissa = (mantissa >> shift) << shift;
+  //  int32_t result = new_mantissa | exponent | sign;
+  //  return bititof(result);
+
+  Node* int_input = Unop(wasm::kExprI32ReinterpretF32, input);
+  Node* exponent =
+      Binop(wasm::kExprI32And, int_input, jsgraph()->Int32Constant(0x7f800000));
+
+  Node* sign =
+      Binop(wasm::kExprI32And, int_input, jsgraph()->Int32Constant(0x80000000));
+
+  Node* result_out_of_range = int_input;
+
+  Node* result_nan =
+      Binop(wasm::kExprI32Ior, int_input, jsgraph()->Int32Constant(1 << 22));
+
+  Node* result_zero = sign;
+
+  Node* mantissa =
+      Binop(wasm::kExprI32And, int_input, jsgraph()->Int32Constant(0x007fffff));
+  Node* shift =
+      Binop(wasm::kExprI32Sub, jsgraph()->Int32Constant(23 + 127),
+            Binop(wasm::kExprI32ShrU, exponent, jsgraph()->Int32Constant(23)));
+  Node* new_mantissa = Binop(wasm::kExprI32Shl,
+                             Binop(wasm::kExprI32ShrU, mantissa, shift), shift);
+  Node* result_truncate =
+      Binop(wasm::kExprI32Ior, Binop(wasm::kExprI32Ior, new_mantissa, exponent),
+            sign);
+
+  Diamond is_zero(
+      graph(), jsgraph()->common(),
+      Binop(wasm::kExprI32LtU, exponent, jsgraph()->Int32Constant(127 << 23)));
+
+  Node* result_within_range =
+      is_zero.Phi(wasm::kAstI32, result_zero, result_truncate);
+
+  Diamond input_nan(graph(), jsgraph()->common(),
+                    Binop(wasm::kExprF32Ne, input, input));
+  Node* result_exponent_geq_23 =
+      input_nan.Phi(wasm::kAstI32, result_nan, result_out_of_range);
+
+  Diamond exponent_geq_23(graph(), jsgraph()->common(),
+                          Binop(wasm::kExprI32GeU, exponent,
+                                jsgraph()->Int32Constant((23 + 127) << 23)));
+
+  Node* result = exponent_geq_23.Phi(wasm::kAstI32, result_exponent_geq_23,
+                                     result_within_range);
+
+  return Unop(wasm::kExprF32ReinterpretI32, result);
+}
+
+
 Node* WasmGraphBuilder::BuildWasmCall(wasm::FunctionSig* sig, Node** args) {
   const size_t params = sig->parameter_count();
   const size_t extra = 2;  // effect and control inputs.