ART: skip compilation of huge methods.

Besides not being worthwhile to compile, it huge methods could cause
overflow of some internal compiler structures.

internal b/17524219

Change-Id: I0e47ff4757eec265809598830a2616ac367af77d
diff --git a/compiler/dex/frontend.cc b/compiler/dex/frontend.cc
index 2ba320f..45fc19e 100644
--- a/compiler/dex/frontend.cc
+++ b/compiler/dex/frontend.cc
@@ -623,11 +623,22 @@
                                      jobject class_loader, const DexFile& dex_file,
                                      void* llvm_compilation_unit) {
   VLOG(compiler) << "Compiling " << PrettyMethod(method_idx, dex_file) << "...";
-  if (code_item->insns_size_in_code_units_ >= 0x10000) {
-    LOG(INFO) << "Method size exceeds compiler limits: " << code_item->insns_size_in_code_units_
+  /*
+   * Skip compilation for pathologically large methods - either by instruction count or num vregs.
+   * Dalvik uses 16-bit uints for instruction and register counts.  We'll limit to a quarter
+   * of that, which also guarantees we cannot overflow our 16-bit internal SSA name space.
+   */
+  if (code_item->insns_size_in_code_units_ >= UINT16_MAX / 4) {
+    LOG(INFO) << "Method exceeds compiler instruction limit: "
+              << code_item->insns_size_in_code_units_
               << " in " << PrettyMethod(method_idx, dex_file);
     return NULL;
   }
+  if (code_item->registers_size_ >= UINT16_MAX / 4) {
+    LOG(INFO) << "Method exceeds compiler virtual register limit: "
+              << code_item->registers_size_ << " in " << PrettyMethod(method_idx, dex_file);
+    return NULL;
+  }
 
   if (!driver.GetCompilerOptions().IsCompilationEnabled()) {
     return nullptr;