[lld-macho] Don't emit spurious dupe method warnings for +load methods

[int3]

Summary

+load methods are static initializers and treated specially by the
runtime: all +load methods for a class & its categories are called when
loading that class, unlike regular methods where only one definition
will get called per message. Thus, there is no need to check for
duplicates.

[oontvoo]

Thanks!

lld/MachO/ObjC.cpp

void ObjcCategoryChecker::parseMethods(const ConcatInputSection *methodsIsec,
                                        MethodKind mKind) {
   ObjcClass &klass = classMap[methodContainerSym];
   for (const Reloc &r : methodsIsec->relocs) {
     if ((r.offset - listHeaderLayout.totalSize) % methodLayout.totalSize !=
         methodLayout.nameOffset)
       continue;
 
     CachedHashStringRef methodName(getReferentString(r));
+    // +load methods are special: all implementations are called by the runtime
+    // even if they are part of the same class. Thus there is no need to check
+    // for duplicates.
+    // NOTE: Instead of specifically checking for this method name, ld64 simply
+    // checks whether a class / category is present in __objc_nlclslist /
+    // __objc_nlcatlist respectively. This will be the case if the class /
+    // category has a +load method. It skips optimizing the categories if there
+    // are multiple +load methods. Since it does dupe checking as part of the
+    // optimization process, this avoids spurious dupe messages around +load,
+    // but it also means that legit dupe issues for other methods are ignored.
+    if (mKind == MK_Static && methodName.val() == "load")
+      continue;
+
     auto &methodMap =
         mKind == MK_Instance ? klass.instanceMethods : klass.classMethods;
     if (methodMap
             .try_emplace(methodName, MethodContainer{mcKind, containerIsec})
             .second)
       continue;
 
     // We have a duplicate; generate a warning message.

lld/test/MachO/objc-category-conflicts.s

 # REQUIRES: x86
 # RUN: rm -rf %t; split-file %s %t
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/cat1.s -o %t/cat1.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/cat2.s -o %t/cat2.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/klass.s -o %t/klass.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/cat1.s --defsym MAKE_LOAD_METHOD=1 -o %t/cat1-with-load.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/cat2.s --defsym MAKE_LOAD_METHOD=1 -o %t/cat2-with-load.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/klass.s --defsym MAKE_LOAD_METHOD=1 -o %t/klass-with-load.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/klass-with-no-rodata.s -o %t/klass-with-no-rodata.o
 # RUN: %lld -dylib -lobjc %t/klass.o -o %t/libklass.dylib
 
 # RUN: %no-fatal-warnings-lld -dylib -lobjc %t/klass.o %t/cat1.o %t/cat2.o -o \
 # RUN:   /dev/null 2>&1 | FileCheck %s --check-prefixes=CATCLS,CATCAT
 # RUN: %no-fatal-warnings-lld -dylib -lobjc %t/libklass.dylib %t/cat1.o \
 # RUN:   %t/cat2.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=CATCAT
 
+## Check that we don't emit spurious warnings around the +load method while
+## still emitting the other warnings. Note that we have made separate
+## `*-with-load.s` files for ease of comparison with ld64; ld64 will not warn
+## at all if multiple +load methods are present.
+# RUN: %no-fatal-warnings-lld -dylib -lobjc %t/klass-with-load.o \
+# RUN:   %t/cat1-with-load.o %t/cat2-with-load.o -o /dev/null 2>&1 | \
+# RUN:   FileCheck %s --check-prefixes=CATCLS,CATCAT --implicit-check-not '+load'
+
 ## Regression test: Check that we don't crash.
 # RUN: %no-fatal-warnings-lld -dylib -lobjc %t/klass-with-no-rodata.o -o /dev/null
 
 # CATCLS:      warning: method '+s1' has conflicting definitions:
-# CATCLS-NEXT: >>> defined in category Cat1 from {{.*}}cat1.o
-# CATCLS-NEXT: >>> defined in class Foo from {{.*}}klass.o
+# CATCLS-NEXT: >>> defined in category Cat1 from {{.*}}cat1{{.*}}.o
+# CATCLS-NEXT: >>> defined in class Foo from {{.*}}klass{{.*}}.o
 
 # CATCLS:      warning: method '-m1' has conflicting definitions:
-# CATCLS-NEXT: >>> defined in category Cat1 from {{.*}}cat1.o
-# CATCLS-NEXT: >>> defined in class Foo from {{.*}}klass.o
+# CATCLS-NEXT: >>> defined in category Cat1 from {{.*}}cat1{{.*}}.o
+# CATCLS-NEXT: >>> defined in class Foo from {{.*}}klass{{.*}}.o
 
 # CATCAT:      warning: method '+s2' has conflicting definitions:
-# CATCAT-NEXT: >>> defined in category Cat2 from {{.*}}cat2.o
-# CATCAT-NEXT: >>> defined in category Cat1 from {{.*}}cat1.o
+# CATCAT-NEXT: >>> defined in category Cat2 from {{.*}}cat2{{.*}}.o
+# CATCAT-NEXT: >>> defined in category Cat1 from {{.*}}cat1{{.*}}.o
 
 # CATCAT:      warning: method '-m2' has conflicting definitions:
-# CATCAT-NEXT: >>> defined in category Cat2 from {{.*}}cat2.o
-# CATCAT-NEXT: >>> defined in category Cat1 from {{.*}}cat1.o
+# CATCAT-NEXT: >>> defined in category Cat2 from {{.*}}cat2{{.*}}.o
+# CATCAT-NEXT: >>> defined in category Cat1 from {{.*}}cat1{{.*}}.o
 
 #--- cat1.s
 
 .include "objc-macros.s"
 
 ## @interface Foo(Cat1)
 ## -(void) m1;
 ## -(void) m2;
 ## +(void) s1;
 ## +(void) s2;
 ## @end
 ## 
 ## @implementation Foo(Cat1)
 ## -(void) m1 {}
 ## -(void) m2 {}
 ## +(void) s1 {}
 ## +(void) s2 {}
 ## @end
 
 .section __DATA,__objc_catlist,regular,no_dead_strip
   .quad __OBJC_$_CATEGORY_Foo_$_Cat1
 
+.ifdef MAKE_LOAD_METHOD
+.section __DATA,__objc_nlcatlist,regular,no_dead_strip
+  .quad __OBJC_$_CATEGORY_Foo_$_Cat1
+.endif
+
 .section __DATA,__objc_const
 __OBJC_$_CATEGORY_Foo_$_Cat1:
   .objc_classname "Cat1"
   .quad _OBJC_CLASS_$_Foo
   .quad __OBJC_$_CATEGORY_INSTANCE_METHODS_Foo_$_Cat1
   .quad __OBJC_$_CATEGORY_CLASS_METHODS_Foo_$_Cat1
   .quad 0
   .quad 0
   .quad 0
   .long 64
   .space 4
 
 __OBJC_$_CATEGORY_INSTANCE_METHODS_Foo_$_Cat1:
   .long 24 # size of method entry
   .long 2 # number of methods
   .empty_objc_method "m1", "v16@0:8", "-[Foo(Cat1) m1]"
   .empty_objc_method "m2", "v16@0:8", "-[Foo(Cat2) m2]"
 
 __OBJC_$_CATEGORY_CLASS_METHODS_Foo_$_Cat1:
   .long 24
+.ifdef MAKE_LOAD_METHOD
+  .long 3
+  .empty_objc_method "load", "v16@0:8", "+[Foo(Cat1) load]"
+.else
   .long 2
+.endif
   .empty_objc_method "s1", "v16@0:8", "+[Foo(Cat1) s1]"
   .empty_objc_method "s2", "v16@0:8", "+[Foo(Cat1) s2]"
 
 .section __DATA,__objc_imageinfo,regular,no_dead_strip
   .long 0
   .long 64
 
 .subsections_via_symbols

 ## @implementation Foo(Cat2)
 ## -(void) m2 {}
 ## +(void) s2 {}
 ## @end
 
 .section __DATA,__objc_catlist,regular,no_dead_strip
   .quad __OBJC_$_CATEGORY_Foo_$_Cat2
 
+.ifdef MAKE_LOAD_METHOD
+.section __DATA,__objc_nlcatlist,regular,no_dead_strip
+  .quad __OBJC_$_CATEGORY_Foo_$_Cat2
+.endif
+
 .section __DATA,__objc_const
 __OBJC_$_CATEGORY_Foo_$_Cat2:
   .objc_classname "Cat2"
   .quad _OBJC_CLASS_$_Foo
   .quad __OBJC_$_CATEGORY_INSTANCE_METHODS_Foo_$_Cat2
   .quad __OBJC_$_CATEGORY_CLASS_METHODS_Foo_$_Cat2
   .quad 0
   .quad 0
   .quad 0
   .long 64
   .space 4
 
 __OBJC_$_CATEGORY_INSTANCE_METHODS_Foo_$_Cat2:
   .long 24
   .long 1
   .empty_objc_method "m2", "v16@0:8", "-[Foo(Cat2) m2]"
 
 __OBJC_$_CATEGORY_CLASS_METHODS_Foo_$_Cat2:
   .long 24
+.ifdef MAKE_LOAD_METHOD
+  .long 2
+  .empty_objc_method "load", "v16@0:8", "+[Foo(Cat2) load]"
+.else
   .long 1
+.endif
   .empty_objc_method "s2", "v16@0:8", "+[Foo(Cat2) m2]"
 
 .section __DATA,__objc_imageinfo,regular,no_dead_strip
   .long 0
   .long 64
 
 .subsections_via_symbols
 
__OBJC_CLASS_RO_$_Foo:
   .quad __OBJC_$_INSTANCE_METHODS_Foo
   .quad 0
   .quad 0
   .quad 0
   .quad 0
 
 __OBJC_$_CLASS_METHODS_Foo:
   .long 24
+.ifdef MAKE_LOAD_METHOD
+  .long 2
+  .empty_objc_method "load", "v16@0:8", "+[Foo load]"
+.else
   .long 1
+.endif
   .empty_objc_method "s1", "v16@0:8", "+[Foo s1]"
 
 __OBJC_$_INSTANCE_METHODS_Foo:
   .long 24
   .long 1
   .empty_objc_method "m1", "v16@0:8", "-[Foo m1]"
 
 .section __DATA,__objc_classlist,regular,no_dead_strip
   .quad _OBJC_CLASS_$_Foo
 
+.ifdef MAKE_LOAD_METHOD
+.section __DATA,__objc_nlclslist,regular,no_dead_strip
+  .quad _OBJC_CLASS_$_Foo
+.endif
+
 .section __DATA,__objc_imageinfo,regular,no_dead_strip
   .long 0
   .long 64
 
 .subsections_via_symbols
 
 #--- klass-with-no-rodata.s