Error with Huge array requirement

**Type of issue**: Bug Report

**Please provide the steps to reproduce the problem:**

I get the Error `java.lang.OutOfMemoryError: Required array length 2147483640 + 18 is too large` when I try to generate a gemmini model with 64x64 PEs, it seems that the chisel3 gets error during the firrtl stage. However, the JAVA VM sets the array's size to be smaller than 2^32 -1 , so how can I generate the RTL with a large parameter?

**Please tell us about your environment:**
version: `3.5.2`
OS: ubuntu 18.04 with 256GB memory.
chipyard version: 1.8.1

```
Output clock buildtop_reference_clock, requested: 100.0 MHz, actual: 100.0 MHz (division of 1)
[error] (run-main-0) java.lang.OutOfMemoryError: Required array length 2147483640 + 18 is too large
[error] java.lang.OutOfMemoryError: Required array length 2147483640 + 18 is too large
[error] at java.base/jdk.internal.util.ArraysSupport.hugeLength(ArraysSupport.java:649)
[error] at java.base/jdk.internal.util.ArraysSupport.newLength(ArraysSupport.java:642)
[error] at java.base/java.lang.AbstractStringBuilder.newCapacity(AbstractStringBuilder.java:257)
[error] at java.base/java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:229)
[error] at java.base/java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:582)
[error] at java.base/java.lang.StringBuilder.append(StringBuilder.java:179)
[error] at scala.collection.mutable.StringBuilder.$plus$plus$eq(StringBuilder.scala:183)
[error] at firrtl.ir.Serializer$.s(Serializer.scala:72)
[error] at firrtl.ir.Serializer$.s(Serializer.scala:299)
[error] at firrtl.ir.Serializer$.s(Serializer.scala:74)
[error] at firrtl.ir.Serializer$.s(Serializer.scala:96)
[error] at firrtl.ir.Serializer$.s(Serializer.scala:110)
[error] at firrtl.ir.Serializer$.s(Serializer.scala:246)
[error] at firrtl.ir.Serializer$.$anonfun$s$9(Serializer.scala:260)
[error] at firrtl.ir.Serializer$.$anonfun$s$9$adapted(Serializer.scala:260)
[error] at scala.collection.immutable.Stream.foreach(Stream.scala:533)
[error] at firrtl.ir.Serializer$.s(Serializer.scala:260)
[error] at firrtl.ir.Serializer$.serialize(Serializer.scala:36)
[error] at firrtl.ir.Serializer$.serialize(Serializer.scala:17)
[error] at chisel3.internal.firrtl.Emitter$.emit(Emitter.scala:11)
[error] at chisel3.stage.phases.Emitter.$anonfun$transform$1(Emitter.scala:45)
[error] at scala.collection.TraversableLike.$anonfun$flatMap$1(TraversableLike.scala:245)
[error] at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:62)
[error] at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:55)
[error] at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:49)
[error] at scala.collection.TraversableLike.flatMap(TraversableLike.scala:245)
[error] at scala.collection.TraversableLike.flatMap$(TraversableLike.scala:242)
[error] at scala.collection.AbstractTraversable.flatMap(Traversable.scala:108)
[error] at chisel3.stage.phases.Emitter.transform(Emitter.scala:42)
[error] at chisel3.stage.phases.Emitter.transform(Emitter.scala:25)
[error] at firrtl.options.phases.DeletedWrapper.internalTransform(DeletedWrapper.scala:38)
[error] at firrtl.options.phases.DeletedWrapper.internalTransform(DeletedWrapper.scala:15)
[error] at firrtl.options.Translator.transform(Phase.scala:248)
[error] at firrtl.options.Translator.transform$(Phase.scala:248)
[error] at firrtl.options.phases.DeletedWrapper.transform(DeletedWrapper.scala:15)
[error] at firrtl.options.DependencyManager.$anonfun$transform$5(DependencyManager.scala:280)
[error] at firrtl.Utils$.time(Utils.scala:181)
[error] at firrtl.options.DependencyManager.$anonfun$transform$3(DependencyManager.scala:280)
[error] at scala.collection.LinearSeqOptimized.foldLeft(LinearSeqOptimized.scala:126)
[error] at scala.collection.LinearSeqOptimized.foldLeft$(LinearSeqOptimized.scala:122)
[error] at scala.collection.immutable.List.foldLeft(List.scala:89)
[error] at firrtl.options.DependencyManager.transform(DependencyManager.scala:269)
[error] at firrtl.options.DependencyManager.transform$(DependencyManager.scala:255)
[error] at firrtl.options.PhaseManager.transform(DependencyManager.scala:443)
[error] at chisel3.stage.ChiselStage.run(ChiselStage.scala:45)
[error] at firrtl.options.Stage$$anon$1.transform(Stage.scala:43)
[error] at firrtl.options.Stage$$anon$1.transform(Stage.scala:43)
[error] at firrtl.options.phases.DeletedWrapper.internalTransform(DeletedWrapper.scala:38)
[error] at firrtl.options.phases.DeletedWrapper.internalTransform(DeletedWrapper.scala:15)
[error] at firrtl.options.Translator.transform(Phase.scala:248)
[error] at firrtl.options.Translator.transform$(Phase.scala:248)
[error] at firrtl.options.phases.DeletedWrapper.transform(DeletedWrapper.scala:15)
[error] at firrtl.options.Stage.$anonfun$transform$5(Stage.scala:47)
[error] at scala.collection.LinearSeqOptimized.foldLeft(LinearSeqOptimized.scala:126)
[error] at scala.collection.LinearSeqOptimized.foldLeft$(LinearSeqOptimized.scala:122)
[error] at scala.collection.immutable.List.foldLeft(List.scala:89)
[error] at firrtl.options.Stage.$anonfun$transform$3(Stage.scala:47)
[error] at logger.Logger$.$anonfun$makeScope$2(Logger.scala:137)
[error] at scala.util.DynamicVariable.withValue(DynamicVariable.scala:62)
[error] at logger.Logger$.makeScope(Logger.scala:135)
[error] at firrtl.options.Stage.transform(Stage.scala:47)
[error] at firrtl.options.Stage.transform(Stage.scala:17)
[error] at firrtl.options.phases.DeletedWrapper.internalTransform(DeletedWrapper.scala:38)
[error] at firrtl.options.phases.DeletedWrapper.internalTransform(DeletedWrapper.scala:15)
[error] at firrtl.options.Translator.transform(Phase.scala:248)
[error] at firrtl.options.Translator.transform$(Phase.scala:248)
[error] at firrtl.options.phases.DeletedWrapper.transform(DeletedWrapper.scala:15)
[error] at firrtl.options.DependencyManager.$anonfun$transform$5(DependencyManager.scala:280)
[error] at firrtl.Utils$.time(Utils.scala:181)
[error] at firrtl.options.DependencyManager.$anonfun$transform$3(DependencyManager.scala:280)
[error] at scala.collection.LinearSeqOptimized.foldLeft(LinearSeqOptimized.scala:126)
[error] at scala.collection.LinearSeqOptimized.foldLeft$(LinearSeqOptimized.scala:122)
[error] at scala.collection.immutable.List.foldLeft(List.scala:89)
[error] at firrtl.options.DependencyManager.transform(DependencyManager.scala:269)
[error] at firrtl.options.DependencyManager.transform$(DependencyManager.scala:255)
[error] at firrtl.options.PhaseManager.transform(DependencyManager.scala:443)
[error] at chisel3.stage.ChiselStage.run(ChiselStage.scala:45)
[error] at firrtl.options.Stage$$anon$1.transform(Stage.scala:43)
[error] at firrtl.options.Stage$$anon$1.transform(Stage.scala:43)
[error] at firrtl.options.phases.DeletedWrapper.internalTransform(DeletedWrapper.scala:38)
[error] at firrtl.options.phases.DeletedWrapper.internalTransform(DeletedWrapper.scala:15)
[error] at firrtl.options.Translator.transform(Phase.scala:248)
[error] at firrtl.options.Translator.transform$(Phase.scala:248)
[error] at firrtl.options.phases.DeletedWrapper.transform(DeletedWrapper.scala:15)
[error] at firrtl.options.Stage.$anonfun$transform$5(Stage.scala:47)
[error] at scala.collection.LinearSeqOptimized.foldLeft(LinearSeqOptimized.scala:126)
[error] at scala.collection.LinearSeqOptimized.foldLeft$(LinearSeqOptimized.scala:122)
[error] at scala.collection.immutable.List.foldLeft(List.scala:89)
[error] at firrtl.options.Stage.$anonfun$transform$3(Stage.scala:47)
[error] at logger.Logger$.$anonfun$makeScope$2(Logger.scala:137)
[error] at scala.util.DynamicVariable.withValue(DynamicVariable.scala:62)
[error] at logger.Logger$.makeScope(Logger.scala:135)
[error] at firrtl.options.Stage.transform(Stage.scala:47)
[error] at firrtl.options.Stage.execute(Stage.scala:58)
[error] at firrtl.options.StageMain.main(Stage.scala:71)
[error] at chipyard.Generator.main(Generator.scala)
[error] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[error] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
[error] at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[error] at java.base/java.lang.reflect.Method.invoke(Method.java:568)
[error] stack trace is suppressed; run last Compile / bgRunMain for the full output
[error] Nonzero exit code: 1
[error] (Compile / runMain) Nonzero exit code: 1
```