Emit VMLA for multiply-add on ARM

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index 17f3325b754c3449f682425313062cf438c8d581..73f377bf365d1e5250390917bbd27dae469088c5 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1303,8 +1303,21 @@ LInstruction* LChunkBuilder::DoMul(HMul* instr) {
     return DefineAsRegister(mul);
 
   } else if (instr->representation().IsDouble()) {
-    return DoArithmeticD(Token::MUL, instr);
+    if (instr->UseCount() == 1 && instr->uses().value()->IsAdd()) {
+      HAdd* add = HAdd::cast(instr->uses().value());
+      if (instr == add->left()) {
+        // This mul is the lhs of an add. The add and mul will be folded
+        // into a multiply-add.
+        return NULL;
+      }
+      if (instr == add->right() && !add->left()->IsMul()) {
+        // This mul is the rhs of an add, where the lhs is not another mul.
+        // The add and mul will be folded into a multiply-add.
+        return NULL;
+      }
+    }
 
+    return DoArithmeticD(Token::MUL, instr);
   } else {
     return DoArithmeticT(Token::MUL, instr);
   }
@@ -1330,6 +1343,13 @@ LInstruction* LChunkBuilder::DoSub(HSub* instr) {
   }
 }
 
+LInstruction* LChunkBuilder::DoMultiplyAdd(HMul* mul, HValue* addend) {
+  LOperand* multiplier_op = UseRegisterAtStart(mul->left());
+  LOperand* multiplicand_op = UseRegisterAtStart(mul->right());
+  LOperand* addend_op = UseRegisterAtStart(addend);
+  return DefineSameAsFirst(new(zone()) LMultiplyAddD(addend_op, multiplier_op,
+                                                     multiplicand_op));
+}
 
 LInstruction* LChunkBuilder::DoAdd(HAdd* instr) {
   if (instr->representation().IsInteger32()) {
@@ -1344,6 +1364,14 @@ LInstruction* LChunkBuilder::DoAdd(HAdd* instr) {
     }
     return result;
   } else if (instr->representation().IsDouble()) {
+    if (instr->left()->IsMul())
+      return DoMultiplyAdd(HMul::cast(instr->left()), instr->right());
+
+    if (instr->right()->IsMul()) {
+      ASSERT(!instr->left()->IsMul());
+      return DoMultiplyAdd(HMul::cast(instr->right()), instr->left());
+    }
+
     return DoArithmeticD(Token::ADD, instr);
   } else {
     ASSERT(instr->representation().IsTagged());