[ThinLTO] Disallow multiple prevailing defs

[tejohnson]

LGTM

lib/LTO/LTO.cpp

void LTO::addModuleToGlobalRes(ArrayRef<InputFile::Symbol> Syms,
   (void)ResE;
   for (const InputFile::Symbol &Sym : Syms) {
     assert(ResI != ResE);
     SymbolResolution Res = *ResI++;
 
     auto &GlobalRes = GlobalResolutions[Sym.getName()];
     GlobalRes.UnnamedAddr &= Sym.isUnnamedAddr();
     if (Res.Prevailing) {
-      assert((GlobalRes.IRName.empty() || !Sym.getIRName().empty()) &&
-             "Overriding existing resolution with undefined asm symbol");
+      assert(GlobalRes.IRName.empty() &&
+             "Multiple prevailing defs are not allowed");
       GlobalRes.IRName = Sym.getIRName();
     }
 
     // Set the partition to external if we know it is re-defined by the linker
     // with -defsym or -wrap options, used elsewhere, e.g. it is visible to a
     // regular object, is referenced from llvm.compiler_used, or was already
     // recorded as being referenced from a different partition.
     if (Res.LinkerRedefined || Res.VisibleToRegularObj || Sym.isUsed() ||

test/LTO/Resolution/X86/common2.ll

 ; Same as before, but reversing the order of the inputs
 ; RUN: llvm-lto2 run %t2.bc %t1.bc -o %t.o -save-temps \
 ; RUN:  -r %t1.bc,v,x \
 ; RUN:  -r %t2.bc,v,x \
 ; RUN:  -r %t1.bc,foo,px \
 ; RUN:  -r %t2.bc,bar,px
 ; RUN: llvm-dis < %t.o.0.0.preopt.bc | FileCheck  %s --check-prefix=NONE-PREVAILED2
 
-
-
-; Client marked both as prevailing
-; RUN: llvm-lto2 run %t1.bc %t2.bc -o %t.o -save-temps \
-; RUN:  -r %t1.bc,v,px \
-; RUN:  -r %t2.bc,v,px \
-; RUN:  -r %t1.bc,foo,px \
-; RUN:  -r %t2.bc,bar,px
-; RUN: llvm-dis < %t.o.0.0.preopt.bc | FileCheck %s --check-prefix=BOTH-PREVAILED1
-
-; Same as before, but reversing the order of the inputs
-; RUN: llvm-lto2 run %t2.bc %t1.bc -o %t.o -save-temps \
-; RUN:  -r %t1.bc,v,px \
-; RUN:  -r %t2.bc,v,px \
-; RUN:  -r %t1.bc,foo,px \
-; RUN:  -r %t2.bc,bar,px
-; RUN: llvm-dis < %t.o.0.0.preopt.bc | FileCheck %s --check-prefix=BOTH-PREVAILED2
-
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 @v = common global i8 0, align 8
 
 ; LARGE-PREVAILED: @v = common global i16 0, align 8
 ; SMALL-PREVAILED: @v = common global [2 x i8] zeroinitializer, align 8
 ; BOTH-PREVAILED1: @v = common global i16 0, align 8
 ; BOTH-PREVAILED2: common global [2 x i8] zeroinitializer, align 8
 ; In this case the first is kept as external
 ; NONE-PREVAILED1: @v = external global i8, align 8
 ; NONE-PREVAILED2: @v = external global i16, align 4
 
 define i8 *@foo() {
  ret i8 *@v
 }

test/LTO/Resolution/X86/dead-strip-fulllto.ll

 ; RUN: opt -module-summary -o %t %s
 ; RUN: opt -module-summary -o %t2 %S/Inputs/dead-strip-fulllto.ll
 
 ; RUN: llvm-lto2 run %t -r %t,main,px -r %t,live1,p -r %t,live2,p -r %t,dead2,p \
-; RUN:               %t2 -r %t2,live1,p -r %t2,live2, -r %t2,dead1,p -r %t2,dead2, -r %t2,odr, \
+; RUN:               %t2 -r %t2,live1, -r %t2,live2, -r %t2,dead1,p -r %t2,dead2, -r %t2,odr, \
 ; RUN: -save-temps -o %t3
 ; RUN: llvm-nm %t3.0 | FileCheck --check-prefix=FULL %s
 ; RUN: llvm-nm %t3.1 | FileCheck --check-prefix=THIN %s
 
 ; RUN: llvm-lto2 run %t -r %t,main,px -r %t,live1,p -r %t,live2,p -r %t,dead2,p \
-; RUN:               %t2 -r %t2,live1,p -r %t2,live2, -r %t2,dead1,p -r %t2,dead2, -r %t2,odr, \
+; RUN:               %t2 -r %t2,live1, -r %t2,live2, -r %t2,dead1,p -r %t2,dead2, -r %t2,odr, \
 ; RUN: -save-temps -o %t3 -O0
 ; RUN: llvm-nm %t3.0 | FileCheck --check-prefix=FULL %s
 ; RUN: llvm-nm %t3.1 | FileCheck --check-prefix=THIN %s
 
 ; FULL-NOT: dead
 ; FULL: U live1
 ; FULL: T live2
 ; FULL: T main

test/ThinLTO/X86/deadstrip.ll

 ; RUN: llvm-lto2 run %t1.bc %t2.bc -o %t.out -save-temps \
 ; RUN:   -r %t1.bc,_main,plx \
 ; RUN:   -r %t1.bc,_bar,pl \
 ; RUN:   -r %t1.bc,_dead_func,pl \
 ; RUN:   -r %t1.bc,_baz,l \
 ; RUN:   -r %t1.bc,_boo,l \
 ; RUN:   -r %t2.bc,_baz,pl \
 ; RUN:   -r %t2.bc,_boo,pl \
-; RUN:   -r %t2.bc,_dead_func,pl \
+; RUN:   -r %t2.bc,_dead_func,l \
 ; RUN:   -r %t2.bc,_another_dead_func,pl
 ; RUN: llvm-dis < %t.out.0.3.import.bc | FileCheck %s --check-prefix=LTO2
 ; RUN: llvm-dis < %t.out.1.3.import.bc | FileCheck %s --check-prefix=LTO2-CHECK2
 ; RUN: llvm-nm %t.out.1 | FileCheck %s --check-prefix=CHECK2-NM
 
 ; RUN: llvm-bcanalyzer -dump %t.out.index.bc | FileCheck %s --check-prefix=COMBINED
 ; Live, NotEligibleForImport, Internal
 ; COMBINED-DAG: <COMBINED {{.*}} op2=55

 ; RUN: llvm-lto2 run %t1.bc %t3.bc -o %t4.out -save-temps \
 ; RUN:   -r %t1.bc,_main,plx \
 ; RUN:   -r %t1.bc,_bar,pl \
 ; RUN:   -r %t1.bc,_dead_func,pl \
 ; RUN:   -r %t1.bc,_baz,l \
 ; RUN:   -r %t1.bc,_boo,l \
 ; RUN:   -r %t3.bc,_baz,pl \
 ; RUN:   -r %t3.bc,_boo,pl \
-; RUN:   -r %t3.bc,_dead_func,pl \
+; RUN:   -r %t3.bc,_dead_func,l \
 ; RUN:   -r %t3.bc,_another_dead_func,pl
 ; RUN: llvm-dis < %t4.out.1.3.import.bc | FileCheck %s --check-prefix=CHECK-NOTDEAD
 ; RUN: llvm-nm %t4.out.0 | FileCheck %s --check-prefix=CHECK-NM-NOTDEAD
 
 ; We can't internalize @dead_func because of the use in the regular LTO
 ; partition.
 ; CHECK-NOTDEAD: define dso_local void @dead_func()
 ; We also can't eliminate @baz because it is in the regular LTO partition