[turbofan] Fix optimized lowering of Math.imul.

src/compiler/simplified-lowering.cc

Index: src/compiler/simplified-lowering.cc
diff --git a/src/compiler/simplified-lowering.cc b/src/compiler/simplified-lowering.cc
index afad38b0c4ffb81744c4b98bab362c221671ffcb..a76d3e2013fd791c04f6b0834df5611ff4cc6344 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -1043,6 +1043,12 @@ class RepresentationSelector {
         if (lower()) NodeProperties::ChangeOp(node, Uint32Op(node));
         break;
       }
+      case IrOpcode::kNumberImul: {
+        VisitBinop(node, UseInfo::TruncatingWord32(),
+                   UseInfo::TruncatingWord32(), MachineRepresentation::kWord32);
+        if (lower()) NodeProperties::ChangeOp(node, Uint32Op(node));
+        break;
+      }
       case IrOpcode::kNumberCeil: {
         VisitUnop(node, UseInfo::TruncatingFloat64(),
                   MachineRepresentation::kFloat64);