Fix large functions debug info by default.

Summary:
Turn on -fix-debuginfo-large-functions by default.

In the process of testing I've discovered that we output cold code
for functions that were too large to be emitted. Fixed that.

(cherry picked from FBD3372697)

bolt/RewriteInstance.cpp

@@ -125,9 +125,11 @@ UpdateDebugSections("update-debug-sections",
 
 static cl::opt<bool>
 FixDebugInfoLargeFunctions("fix-debuginfo-large-functions",
+                           cl::init(true),
                            cl::desc("do another pass if we encounter large "
                                     "functions, to correct their debug info."),
-                           cl::Optional);
+                           cl::Optional,
+                           cl::ReallyHidden);
 
 static cl::opt<bool>
 AlignBlocks("align-blocks",
@@ -1306,6 +1308,7 @@ void RewriteInstance::emitFunctions() {
     if (!Function.isSimple())
       continue;
 
+    auto TooLarge = false;
     auto SMII = EFMM->SectionMapInfo.find(Function.getCodeSectionName());
     if (SMII != EFMM->SectionMapInfo.end()) {
       DEBUG(dbgs() << "BOLT: mapping 0x"
@@ -1317,6 +1320,10 @@ void RewriteInstance::emitFunctions() {
                             Function.getAddress());
       Function.setImageAddress(SMII->second.AllocAddress);
       Function.setImageSize(SMII->second.Size);
+      if (Function.getImageSize() > Function.getMaxSize()) {
+        TooLarge = true;
+        FailedAddresses.emplace_back(Function.getAddress());
+      }
     } else {
       errs() << "BOLT: cannot remap function " << Function.getName() << "\n";
       FailedAddresses.emplace_back(Function.getAddress());
@@ -1340,10 +1347,10 @@ void RewriteInstance::emitFunctions() {
                             NextAvailableAddress);
       Function.cold().setAddress(NextAvailableAddress);
       Function.cold().setImageAddress(SMII->second.AllocAddress);
-      Function.cold().setImageSize(SMII->second.Size);
+      Function.cold().setImageSize(TooLarge ? 0 : SMII->second.Size);
       Function.cold().setFileOffset(getFileOffsetFor(NextAvailableAddress));
 
-      NextAvailableAddress += SMII->second.Size;
+      NextAvailableAddress += Function.cold().getImageSize();
     } else {
       errs() << "BOLT: cannot remap function " << Function.getName() << "\n";
       FailedAddresses.emplace_back(Function.getAddress());