[lld-macho][nfc] Add test for resolution of bitcode symbols

[int3]

Summary

We lacked a test for bitcode symbol precedence. We assumed that
they followed the same rules as their regular symbol counterparts, but
never had a test to verify that we were matching ld64's behavior. It
turns out that we were largely correct, though we deviate from ld64 when
there are bitcode and non-bitcode symbols of the same name. The test
added in this diff both verifies our behavior and documents the
differences.

[thakis]

Nice!

lld/test/MachO/lto-symbol-resolution.ll

+; REQUIRES: x86
+
+; RUN: rm -rf %t; split-file %s %t
+
+; RUN: opt -module-summary %t/defined.ll -o %t/defined.o
+; RUN: opt -module-summary %t/weak-defined.ll -o %t/weak-defined.o
+; RUN: opt -module-summary %t/archive.ll -o %t/archive.o
+; RUN: opt -module-summary %t/calls-foo.ll -o %t/calls-foo.o
+; RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/weak-defined.s -o %t/weak-defined-asm.o
+
+; RUN: %lld -lSystem -dylib %t/defined.o -o %t/libfoo.dylib
+; RUN: %lld -lSystem -dylib %t/weak-defined.o -o %t/libweakfoo.dylib
+
+; RUN: llvm-ar rcs %t/archive.a %t/archive.o
+
+;; Regular defined symbols take precedence over weak ones.
+; RUN: %lld -lSystem %t/defined.o %t/weak-defined.o %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=DEFINED
+; RUN: %lld -lSystem %t/weak-defined.o %t/defined.o %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=DEFINED
+
+;; Regular defined symbols take precedence over weak non-bitcode ones.
+; RUN: %lld -lSystem %t/defined.o %t/weak-defined-asm.o %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=DEFINED
+; RUN: %lld -lSystem %t/weak-defined-asm.o %t/defined.o %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=DEFINED
+
+;; NOTE: we are deviating from ld64's behavior here.
+;; ld64: Weak non-bitcode symbols take precedence over weak bitcode ones.
+;; lld: Weak non-bitcode symbols have the same precedence as weak bitcode ones.
+; RUN: %lld -lSystem %t/weak-defined.o %t/weak-defined-asm.o %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=WEAK-DEFINED
+; COM (ld64): llvm-objdump --syms %t/test | FileCheck %s --check-prefix=WEAK-DEFINED-ASM
+; RUN: %lld -lSystem %t/weak-defined-asm.o %t/weak-defined.o %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=WEAK-DEFINED-ASM
+
+;; Weak defined symbols take precedence over dylib symbols.
+; RUN: %lld -lSystem %t/weak-defined.o %t/libfoo.dylib %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=WEAK-DEFINED
+; RUN: %lld -lSystem %t/libfoo.dylib %t/weak-defined.o %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=WEAK-DEFINED
+
+;; Weak defined symbols take precedence over archive symbols.
+; RUN: %lld -lSystem %t/archive.a %t/weak-defined.o %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=WEAK-DEFINED
+; RUN: %lld -lSystem %t/weak-defined.o %t/archive.a %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=WEAK-DEFINED
+
+;; Archive symbols have the same precedence as dylib symbols.
+; RUN: %lld -lSystem %t/archive.a %t/libfoo.dylib %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=ARCHIVE
+; RUN: %lld -lSystem %t/libfoo.dylib %t/archive.a %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=DYLIB
+
+;; Archive symbols take precedence over weak dylib symbols.
+; RUN: %lld -lSystem %t/archive.a %t/libweakfoo.dylib %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=ARCHIVE
+; RUN: %lld -lSystem %t/libweakfoo.dylib %t/archive.a %t/calls-foo.o -o %t/test
+; RUN: llvm-objdump --syms %t/test | FileCheck %s --check-prefix=ARCHIVE
+
+; DEFINED:          g     O __TEXT,defined _foo
+; WEAK-DEFINED:     w     O __TEXT,weak_defined _foo
+; WEAK-DEFINED-ASM: w     O __TEXT,weak_defined_asm _foo
+; ARCHIVE:          g     O __TEXT,archive _foo
+; DYLIB:            *UND* _foo
+
+;--- defined.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.15.0"
+
+define void @foo() section "__TEXT,defined" {
+  ret void
+}
+
+;--- weak-defined.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.15.0"
+
+define weak void @foo() section "__TEXT,weak_defined" {
+  ret void
+}
+
+;--- weak-defined.s
+.globl _foo
+.weak_definition _foo
+.section __TEXT,weak_defined_asm
+_foo:
+
+;--- archive.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.15.0"
+
+define void @foo() section "__TEXT,archive" {
+  ret void
+}
+
+;--- calls-foo.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.15.0"
+
+declare void @foo()
+
+define void @main() {
+  call void @foo()
+  ret void
+}