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[lld-macho] Add support for non-lazy categories to ObjC category merger (#91548)
In ObjC we can have categories that define a `+load` method that is called when the category is loaded. In such cases, we shouldn't optimize the category. These categories are present in the `__objc_nlcatlist` section. So we scan these section for such categories and ignore them from optimization.
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Lines changed: 71 additions & 0 deletions

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‎lld/MachO/ObjC.cpp‎

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@@ -428,6 +428,7 @@ class ObjcCategoryMerger {
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static void doCleanup();
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private:
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DenseSet<const Symbol *> collectNlCategories();
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void collectAndValidateCategoriesData();
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void
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mergeCategoriesIntoSingleCategory(std::vector<InfoInputCategory> &categories);
@@ -1060,7 +1061,27 @@ void ObjcCategoryMerger::createSymbolReference(Defined *refFrom,
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refFrom->isec()->relocs.push_back(r);
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}
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// Get the list of categories in the '__objc_nlcatlist' section. We can't
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// optimize these as they have a '+load' method that has to be called at
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// runtime.
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DenseSet<const Symbol *> ObjcCategoryMerger::collectNlCategories() {
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DenseSet<const Symbol *> nlCategories;
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for (InputSection *sec : allInputSections) {
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if (sec->getName() != section_names::objcNonLazyCatList)
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continue;
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for (auto &r : sec->relocs) {
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const Symbol *sym = r.referent.dyn_cast<Symbol *>();
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nlCategories.insert(sym);
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}
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}
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return nlCategories;
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}
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void ObjcCategoryMerger::collectAndValidateCategoriesData() {
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auto nlCategories = collectNlCategories();
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for (InputSection *sec : allInputSections) {
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if (sec->getName() != section_names::objcCatList)
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continue;
@@ -1074,6 +1095,9 @@ void ObjcCategoryMerger::collectAndValidateCategoriesData() {
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assert(categorySym &&
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"Failed to get a valid category at __objc_catlit offset");
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if (nlCategories.count(categorySym))
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continue;
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// We only support ObjC categories (no swift + @objc)
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// TODO: Support swift + @objc categories also
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if (!categorySym->getName().starts_with(objc::symbol_names::category))

‎lld/test/MachO/objc-category-merging-complete-test.s‎

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@@ -88,6 +88,7 @@ MERGE_CATS-NEXT: name {{.*}} MyProtocol02Prop
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MERGE_CATS-NEXT: attributes {{.*}} Ti,R,D
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MERGE_CATS-NEXT: name {{.*}} MyProtocol03Prop
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MERGE_CATS-NEXT: attributes {{.*}} Ti,R,D
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MERGE_CATS: __OBJC_$_CATEGORY_MyBaseClass_$_Category04
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NO_MERGE_CATS-NOT: __OBJC_$_CATEGORY_MyBaseClass(Category02|Category03)
@@ -431,6 +432,15 @@ L_OBJC_IMAGE_INFO:
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## @dynamic MyProtocol03Prop;
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## @end
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##
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## // This category shouldn't be merged
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## @interface MyBaseClass(Category04)
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## + (void)load;
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## @end
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##
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## @implementation MyBaseClass(Category04)
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## + (void)load {}
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## @end
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##
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## int main() {
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## return 0;
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## }
@@ -493,6 +503,12 @@ L_OBJC_IMAGE_INFO:
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b _OUTLINED_FUNCTION_0
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.cfi_endproc
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; -- End function
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.p2align 2
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"+[MyBaseClass(Category04) load]":
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.cfi_startproc
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; %bb.0:
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ret
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.cfi_endproc
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.globl _main ; -- Begin function main
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.p2align 2
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_main: ; @main
@@ -746,11 +762,42 @@ __OBJC_$_CATEGORY_MyBaseClass_$_Category03:
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.quad 0
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.long 64 ; 0x40
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.space 4
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.section __TEXT,__objc_classname,cstring_literals
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l_OBJC_CLASS_NAME_.15:
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.asciz "Category04"
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.section __TEXT,__objc_methname,cstring_literals
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l_OBJC_METH_VAR_NAME_.16:
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.asciz "load"
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.section __DATA,__objc_const
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.p2align 3, 0x0
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__OBJC_$_CATEGORY_CLASS_METHODS_MyBaseClass_$_Category04:
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.long 24
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.long 1
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.quad l_OBJC_METH_VAR_NAME_.16
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.quad l_OBJC_METH_VAR_TYPE_
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.quad "+[MyBaseClass(Category04) load]"
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.p2align 3, 0x0
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__OBJC_$_CATEGORY_MyBaseClass_$_Category04:
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.quad l_OBJC_CLASS_NAME_.15
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.quad _OBJC_CLASS_$_MyBaseClass
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.quad 0
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.quad __OBJC_$_CATEGORY_CLASS_METHODS_MyBaseClass_$_Category04
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.quad 0
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.quad 0
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.quad 0
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.long 64
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.space 4
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.section __DATA,__objc_catlist,regular,no_dead_strip
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.p2align 3, 0x0 ; @"OBJC_LABEL_CATEGORY_$"
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l_OBJC_LABEL_CATEGORY_$:
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.quad __OBJC_$_CATEGORY_MyBaseClass_$_Category02
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.quad __OBJC_$_CATEGORY_MyBaseClass_$_Category03
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.quad __OBJC_$_CATEGORY_MyBaseClass_$_Category04
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.section __DATA,__objc_nlcatlist,regular,no_dead_strip
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.p2align 3, 0x0
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l_OBJC_LABEL_NONLAZY_CATEGORY_$:
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.quad __OBJC_$_CATEGORY_MyBaseClass_$_Category04
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.no_dead_strip __OBJC_LABEL_PROTOCOL_$_MyProtocol02
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.no_dead_strip __OBJC_LABEL_PROTOCOL_$_MyProtocol03
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.no_dead_strip __OBJC_PROTOCOL_$_MyProtocol02

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