[lld/mac] Search .tbd before binary for framework files too

[thakis]

Summary

This matters for example for the iPhoneSimulator14.0.sdk, which has
a System/Library/Frameworks/UIKit.framework/UIKit that has
LC_BUILD_VERSION with minos of 14.0, so linking against that file
will produce warnings like:

.../iPhoneSimulator14.0.sdk/System/Library/Frameworks/UIKit.framework/UIKit
has version 14.0.0, which is newer than target minimum of 12.0.0

when targeting x86_64-apple-ios12.0-simulator. That doens't happen when
linking against UIKit.tbd instead, obviously.

Linking with RC_TRACE_DYLIB_SEARCHING=1 shows that ld64 also searches
the tbd file first, and we already get that right for non-framework
dylibs.

Fixes crbug.com/1249456.

[int3]

Thanks!

lld/MachO/DriverUtils.cpp

if (config->printDylibSearch)
     message("searched " + path + (found ? ", found " : ", not found"));
   if (!found)
     depTracker->logFileNotFound(path);
 }
 
 Optional<std::string> macho::resolveDylibPath(StringRef dylibPath) {
   // TODO: if a tbd and dylib are both present, we should check to make sure
   // they are consistent.
-  bool dylibExists = fs::exists(dylibPath);
-  searchedDylib(dylibPath, dylibExists);
-  if (dylibExists)
-    return std::string(dylibPath);
-
   SmallString<261> tbdPath = dylibPath;
   path::replace_extension(tbdPath, ".tbd");
   bool tbdExists = fs::exists(tbdPath);
   searchedDylib(tbdPath, tbdExists);
   if (tbdExists)
     return std::string(tbdPath);
+
+  bool dylibExists = fs::exists(dylibPath);
+  searchedDylib(dylibPath, dylibExists);
+  if (dylibExists)
+    return std::string(dylibPath);
   return {};
 }
 
 // It's not uncommon to have multiple attempts to load a single dylib,
 // especially if it's a commonly re-exported core library.
 static DenseMap<CachedHashStringRef, DylibFile *> loadedDylibs;
 
 DylibFile *macho::loadDylib(MemoryBufferRef mbref, DylibFile *umbrella,

lld/test/MachO/link-search-order.s

 # RUN: llvm-objdump --macho --dylibs-used %t/test | FileCheck --check-prefix=DYLIB %s
 # RUN: %lld -L%S/Inputs/MacOSX.sdk/usr/lib -o %t/test -Z \
 # RUN:     -L%tA       -L%t -lhello -lgoodbye -lSystem %t/test.o -search_dylibs_first
 # RUN: llvm-objdump --macho --dylibs-used %t/test | FileCheck --check-prefix=ARCHIVE %s
 # RUN: %lld -L%S/Inputs/MacOSX.sdk/usr/lib -o %t/test -Z \
 # RUN:     -L%tD       -L%t -lhello -lgoodbye -lSystem %t/test.o -search_dylibs_first
 # RUN: llvm-objdump --macho --dylibs-used %t/test | FileCheck --check-prefix=DYLIB %s
 
+################ Test that we try the tbd file before the binary for frameworks too.
+# RUN: not %lld -dylib -F %t -framework Foo -o %t --print-dylib-search \
+# RUN:     | FileCheck --check-prefix=FRAMEWORKSEARCH -DPATH=%t %s
+
 # DYLIB: @executable_path/libhello.dylib
 # DYLIB: @executable_path/libgoodbye.dylib
 # DYLIB: /usr/lib/libSystem.dylib
 
 # DYLIBSEARCH:      searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.tbd, not found
 # DYLIBSEARCH-NEXT: searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.dylib, not found
 # DYLIBSEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.tbd, not found
 # DYLIBSEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.dylib, not found
 # DYLIBSEARCH:      searched [[PATH]]{{[/\\]}}libhello.dylib, found
 # DYLIBSEARCH:      searched [[PATH]]D{{[/\\]}}libgoodbye.dylib, found
 
 # ARCHIVE:     @executable_path/libhello.dylib
 # ARCHIVE-NOT: @executable_path/libgoodbye.dylib
 # ARCHIVE:     /usr/lib/libSystem.dylib
 
 # ARCHIVESEARCH:      searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.tbd, not found
 # ARCHIVESEARCH-NEXT: searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.dylib, not found
 # ARCHIVESEARCH-NEXT: searched {{.*}}/MacOSX.sdk/usr/lib{{[/\\]}}libhello.a, not found
 # ARCHIVESEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.tbd, not found
 # ARCHIVESEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.dylib, not found
 # ARCHIVESEARCH-NEXT: searched [[PATH]]A{{[/\\]}}libhello.a, not found
 # ARCHIVESEARCH:      searched [[PATH]]{{[/\\]}}libhello.dylib, found
 # ARCHIVESEARCH:      searched [[PATH]]A{{[/\\]}}libgoodbye.a, found
 
+# FRAMEWORKSEARCH:      searched [[PATH]]{{[/\\]}}Foo.framework{{[/\\]}}Foo.tbd, not found
+# FRAMEWORKSEARCH-NEXT: searched [[PATH]]{{[/\\]}}Foo.framework{{[/\\]}}Foo, not found
+
 .section __TEXT,__text
 .global _main
 
 _main:
   movl $0x2000004, %eax                         # write()
   mov $1, %rdi                                  # stdout
   movq _hello_world@GOTPCREL(%rip), %rsi
   mov $13, %rdx                                 # length