[Clang] Report an error and crash on source location exhaustion in macros (#69908)

`createExpansionLocImpl` has an assert that checks if we ran out of
source locations. We have observed this happening on real code and in
release builds the assertion does not fire and the compiler just keeps
running indefinitely without giving any indication that something went
wrong.

Diagnose this problem and reliably crash to make sure the problem is
easy to detect.

I have also tried:
- returning invalid source locations,
- reporting sloc address space usage on error.

Both caused the compiler to run indefinitely. It would be nice to dig
further why that happens, but until then crashing seems like a better
alternative.

Author: ilya-biryukov

clang/include/clang/Basic/DiagnosticCommonKinds.td

@@ -356,9 +356,8 @@ def err_file_modified : Error<
   "file '%0' modified since it was first processed">, DefaultFatal;
 def err_file_too_large : Error<
   "sorry, unsupported: file '%0' is too large for Clang to process">;
-def err_include_too_large : Error<
-  "sorry, this include generates a translation unit too large for"
-  " Clang to process.">, DefaultFatal;
+def err_sloc_space_too_large : Error<
+  "sorry, the translation unit is too large for Clang to process: ran out of source locations">, DefaultFatal;
 def err_unsupported_bom : Error<"%0 byte order mark detected in '%1', but "
   "encoding is not supported">, DefaultFatal;
 def err_unable_to_rename_temp : Error<

clang/lib/Basic/SourceManager.cpp

@@ -605,7 +605,7 @@ FileID SourceManager::createFileIDImpl(ContentCache &File, StringRef Filename,
   unsigned FileSize = File.getSize();
   if (!(NextLocalOffset + FileSize + 1 > NextLocalOffset &&
         NextLocalOffset + FileSize + 1 <= CurrentLoadedOffset)) {
-    Diag.Report(IncludePos, diag::err_include_too_large);
+    Diag.Report(IncludePos, diag::err_sloc_space_too_large);
     noteSLocAddressSpaceUsage(Diag);
     return FileID();
   }
@@ -663,10 +663,16 @@ SourceManager::createExpansionLocImpl(const ExpansionInfo &Info,
     return SourceLocation::getMacroLoc(LoadedOffset);
   }
   LocalSLocEntryTable.push_back(SLocEntry::get(NextLocalOffset, Info));
-  // FIXME: Produce a proper diagnostic for this case.
-  assert(NextLocalOffset + Length + 1 > NextLocalOffset &&
-         NextLocalOffset + Length + 1 <= CurrentLoadedOffset &&
-         "Ran out of source locations!");
+  if (NextLocalOffset + Length + 1 <= NextLocalOffset ||
+      NextLocalOffset + Length + 1 > CurrentLoadedOffset) {
+    Diag.Report(SourceLocation(), diag::err_sloc_space_too_large);
+    // FIXME: call `noteSLocAddressSpaceUsage` to report details to users and
+    // use a source location from `Info` to point at an error.
+    // Currently, both cause Clang to run indefinitely, this needs to be fixed.
+    // FIXME: return an error instead of crashing. Returning invalid source
+    // locations causes compiler to run indefinitely.
+    llvm::report_fatal_error("ran out of source locations");
+  }
   // See createFileID for that +1.
   NextLocalOffset += Length + 1;
   return SourceLocation::getMacroLoc(NextLocalOffset - (Length + 1));

clang/test/Lexer/SourceLocationsOverflow.c

@@ -1,6 +1,6 @@
 // RUN: not %clang %s -S -o - 2>&1 | FileCheck %s
 // CHECK: In file included from {{.*}}SourceLocationsOverflow.c
-// CHECK-NEXT: inc1.h{{.*}}: fatal error: sorry, this include generates a translation unit too large for Clang to process.
+// CHECK-NEXT: inc1.h{{.*}}: fatal error: sorry, the translation unit is too large for Clang to process: ran out of source locations
 // CHECK-NEXT: #include "inc2.h"
 // CHECK-NEXT:          ^
 // CHECK-NEXT: note: 214{{.......}}B in local locations, 0B in locations loaded from AST files, for a total of 214{{.......}}B (99% of available space)