[lld] [llvm] [lld] Fix -ObjC load behavior with LTO (PR #92162)

[Nuri Amari via llvm-commits]

https://github.com/NuriAmari created https://github.com/llvm/llvm-project/pull/92162

When -ObjC is passed, the linker must force load any object files that contain special sections that store Objective-C / Swift information that is used at runtime.

This should work regadless if input files are bitcode or native, but it was not working with bitcode. This is because the sections that identify an object file that should be loaded were inconsistent when dealing with a native file vs bitcode file. In particular, bitcode files were not searched for `__TEXT,__swift` prefixed sections, while native files were.

This means LLD wasn't loading certain bitcode files and forcing the user to introduce --force-load to their linker invocation for that archive.

>From fa4ea07529982ebcd19fa1b5bec5720337e76269 Mon Sep 17 00:00:00 2001
From: Nuri Amari <nuriamari at fb.com>
Date: Fri, 10 May 2024 12:34:04 -0700
Subject: [PATCH] [lld] Fix -ObjC load behavior with LTO

When -ObjC is passed, the linker must force load any object files that
contain special sections that store Objective-C / Swift information that
is used at runtime.

This should work regadless if input files are bitcode or native, but
it was not working with bitcode. This is because the sections that
identify an object file that should be loaded were inconsistent when
dealing with a native file vs bitcode file. In particular, bitcode files
were not searched for `__TEXT,__swift` prefixed sections, while native
files were.

This means LLD wasn't loading certain bitcode files and forcing the
user to introduce --force-load to their linker invocation for that
archive.
---
 lld/test/MachO/objc.s                     | 23 ++++++++++++++++++++---
 llvm/lib/Bitcode/Reader/BitcodeReader.cpp |  3 ++-
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/lld/test/MachO/objc.s b/lld/test/MachO/objc.s
index e7074141f0113..dbb9f1df27571 100644
--- a/lld/test/MachO/objc.s
+++ b/lld/test/MachO/objc.s
@@ -5,12 +5,14 @@
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/has-objc-category.s -o %t/has-objc-category.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/has-objc-symbol-and-category.s -o %t/has-objc-symbol-and-category.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/has-swift.s -o %t/has-swift.o
+# RUN: llvm-as %t/has-swift-ir-loaded.ll -o %t/has-swift-ir-loaded.o
+# RUN: llvm-as %t/has-swift-ir-not-loaded.ll -o %t/has-swift-ir-not-loaded.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/has-swift-proto.s -o %t/has-swift-proto.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/no-objc.s -o %t/no-objc.o
 ## Make sure we don't mis-parse a 32-bit file as 64-bit
 # RUN: llvm-mc -filetype=obj -triple=armv7-apple-watchos %t/no-objc.s -o %t/wrong-arch.o
-# RUN: llvm-ar rcs %t/libHasSomeObjC.a %t/no-objc.o %t/has-objc-symbol.o %t/has-objc-category.o %t/has-swift.o %t/has-swift-proto.o %t/wrong-arch.o
-# RUN: llvm-ar rcs %t/libHasSomeObjC2.a %t/no-objc.o %t/has-objc-symbol-and-category.o %t/has-swift.o %t/has-swift-proto.o %t/wrong-arch.o
+# RUN: llvm-ar rcs %t/libHasSomeObjC.a %t/no-objc.o %t/has-objc-symbol.o %t/has-objc-category.o %t/has-swift.o %t/has-swift-proto.o %t/has-swift-ir-loaded.o %t/has-swift-ir-not-loaded.o %t/wrong-arch.o
+# RUN: llvm-ar rcs %t/libHasSomeObjC2.a %t/no-objc.o %t/has-objc-symbol-and-category.o %t/has-swift.o %t/has-swift-proto.o %t/has-swift-ir-loaded.o %t/has-swift-ir-not-loaded.o %t/wrong-arch.o
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
 
@@ -20,7 +22,7 @@
 # RUN: %lld -lSystem %t/test.o -o %t/test -L%t -lHasSomeObjC2 -ObjC
 # RUN: llvm-objdump --section-headers --syms %t/test | FileCheck %s --check-prefix=OBJC
 
-# RUN: %no-fatal-warnings-lld -lSystem %t/test.o -o %t/test --start-lib %t/no-objc.o %t/has-objc-symbol.o %t/has-objc-category.o %t/has-swift.o %t/has-swift-proto.o %t/wrong-arch.o --end-lib -ObjC 2>&1 \
+# RUN: %no-fatal-warnings-lld -lSystem %t/test.o -o %t/test --start-lib %t/no-objc.o %t/has-objc-symbol.o %t/has-objc-category.o %t/has-swift.o %t/has-swift-proto.o %t/has-swift-ir-loaded.o %t/has-swift-ir-not-loaded.o %t/wrong-arch.o --end-lib -ObjC 2>&1 \
 # RUN:     | FileCheck -check-prefix=WARNING %s
 # RUN: llvm-objdump --section-headers --syms %t/test | FileCheck %s --check-prefix=OBJC
 
@@ -36,6 +38,7 @@
 # OBJC-NEXT:    4 has_objc_symbol {{.*}}      DATA
 # OBJC-EMPTY:
 # OBJC-NEXT:  SYMBOL TABLE:
+# OBJC-DAG:   g     O __TEXT,__swift _foo
 # OBJC-DAG:   g     F __TEXT,__text _main
 # OBJC-DAG:   g     F __TEXT,__text _OBJC_CLASS_$_MyObject
 # OBJC-DAG:   g     O __TEXT,__swift5_fieldmd $s7somelib4Blah_pMF
@@ -100,6 +103,20 @@ _has_dup:
 .section __TEXT,__swift
 .quad 0x1234
 
+#--- has-swift-ir-loaded.ll
+target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+target triple = "x86_64-apple-darwin"
+
+ at foo = global i64 1234, section "__TEXT,__swift"
+ at llvm.used = appending global [1 x ptr] [ptr @foo]
+
+#--- has-swift-ir-not-loaded.ll
+target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+target triple = "x86_64-apple-darwin"
+
+ at bar = global i64 1234
+ at llvm.used = appending global [1 x ptr] [ptr @bar]
+
 #--- has-swift-proto.s
 .section __TEXT,__swift5_fieldmd
 .globl $s7somelib4Blah_pMF
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 19a15209f8b66..e64051cf53862 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -306,7 +306,8 @@ static Expected<bool> hasObjCCategoryInModule(BitstreamCursor &Stream) {
         return error("Invalid section name record");
       // Check for the i386 and other (x86_64, ARM) conventions
       if (S.find("__DATA,__objc_catlist") != std::string::npos ||
-          S.find("__OBJC,__category") != std::string::npos)
+          S.find("__OBJC,__category") != std::string::npos ||
+          S.find("__TEXT,__swift") != std::string::npos)
         return true;
       break;
     }