Revert "Use private linkage for MergedGlobals variables" on Darwin.

This is a partial revert of r244615 (http://reviews.llvm.org/D11942),
which caused a major regression in debug info quality.

Turning the artificial __MergedGlobal symbols into private symbols
(l__MergedGlobal) means that the linker will not include them in the
symbol table of the final executable. Without a symbol table entry
dsymutil is not be able to process the debug info for any of the
merged globals and thus drops the debug info for all of them.

This patch is enabling the old behavior for all MachO targets while
leaving all other targets unaffected.

rdar://problem/29160481
https://reviews.llvm.org/D26531

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286607 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/GlobalMerge.cpp

@@ -432,6 +432,8 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
     std::vector<Type*> Tys;
     std::vector<Constant*> Inits;
 
+    bool HasExternal = false;
+    GlobalVariable *TheFirstExternal = nullptr;
     for (j = i; j != -1; j = GlobalSet.find_next(j)) {
       Type *Ty = Globals[j]->getValueType();
       MergedSize += DL.getTypeAllocSize(Ty);
@@ -440,14 +442,34 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
       }
       Tys.push_back(Ty);
       Inits.push_back(Globals[j]->getInitializer());
+
+      if (Globals[j]->hasExternalLinkage() && !HasExternal) {
+        HasExternal = true;
+        TheFirstExternal = Globals[j];
+      }
     }
 
+    // If merged variables doesn't have external linkage, we needn't to expose
+    // the symbol after merging.
+    GlobalValue::LinkageTypes Linkage = HasExternal
+                                            ? GlobalValue::ExternalLinkage
+                                            : GlobalValue::InternalLinkage;
     StructType *MergedTy = StructType::get(M.getContext(), Tys);
     Constant *MergedInit = ConstantStruct::get(MergedTy, Inits);
 
-    GlobalVariable *MergedGV = new GlobalVariable(
-        M, MergedTy, isConst, GlobalValue::PrivateLinkage, MergedInit,
-        "_MergedGlobals", nullptr, GlobalVariable::NotThreadLocal, AddrSpace);
+    // On Darwin external linkage needs to be preserved, otherwise dsymutil
+    // cannot preserve the debug info for the merged variables.  If they have
+    // external linkage, use the symbol name of the first variable merged as the
+    // suffix of global symbol name.  This avoids a link-time naming conflict
+    // for the _MergedGlobals symbols.
+    Twine MergedName =
+        (IsMachO && HasExternal)
+            ? "_MergedGlobals_" + TheFirstExternal->getName()
+            : "_MergedGlobals";
+    auto MergedLinkage = IsMachO ? Linkage : GlobalValue::PrivateLinkage;
+    auto *MergedGV = new GlobalVariable(
+        M, MergedTy, isConst, MergedLinkage, MergedInit, MergedName, nullptr,
+        GlobalVariable::NotThreadLocal, AddrSpace);
 
     const StructLayout *MergedLayout = DL.getStructLayout(MergedTy);
 

test/CodeGen/AArch64/global-merge-1.ll

@@ -12,9 +12,9 @@
 
 define void @f1(i32 %a1, i32 %a2) {
 ;CHECK-APPLE-IOS-NOT: adrp
-;CHECK-APPLE-IOS: adrp	x8, l__MergedGlobals@PAGE
+;CHECK-APPLE-IOS: adrp	x8, __MergedGlobals@PAGE
 ;CHECK-APPLE-IOS-NOT: adrp
-;CHECK-APPLE-IOS: add	x8, x8, l__MergedGlobals@PAGEOFF
+;CHECK-APPLE-IOS: add	x8, x8, __MergedGlobals@PAGEOFF
   store i32 %a1, i32* @m, align 4
   store i32 %a2, i32* @n, align 4
   ret void
@@ -26,6 +26,6 @@ define void @f1(i32 %a1, i32 %a2) {
 ;CHECK: m = .L_MergedGlobals
 ;CHECK: n = .L_MergedGlobals+4
 
-;CHECK-APPLE-IOS: .zerofill __DATA,__bss,l__MergedGlobals,8,3 ; @_MergedGlobals
+;CHECK-APPLE-IOS: .zerofill __DATA,__bss,__MergedGlobals,8,3 ; @_MergedGlobals
 ;CHECK-APPLE-IOS-NOT: _m = l__MergedGlobals
 ;CHECK-APPLE-IOS-NOT: _n = l__MergedGlobals+4

test/CodeGen/AArch64/global-merge-2.ll

@@ -9,8 +9,8 @@
 define void @f1(i32 %a1, i32 %a2) {
 ;CHECK-APPLE-IOS-LABEL: _f1:
 ;CHECK-APPLE-IOS-NOT: adrp
-;CHECK-APPLE-IOS: adrp	x8, l__MergedGlobals@PAGE
-;CHECK-APPLE-IOS: add	x8, x8, l__MergedGlobals@PAGEOFF
+;CHECK-APPLE-IOS: adrp	x8, __MergedGlobals_x@PAGE
+;CHECK-APPLE-IOS: add	x8, x8, __MergedGlobals_x@PAGEOFF
 ;CHECK-APPLE-IOS-NOT: adrp
   store i32 %a1, i32* @x, align 4
   store i32 %a2, i32* @y, align 4
@@ -19,8 +19,8 @@ define void @f1(i32 %a1, i32 %a2) {
 
 define void @g1(i32 %a1, i32 %a2) {
 ;CHECK-APPLE-IOS-LABEL: _g1:
-;CHECK-APPLE-IOS: adrp	x8, l__MergedGlobals@PAGE
-;CHECK-APPLE-IOS: add	x8, x8, l__MergedGlobals@PAGEOFF
+;CHECK-APPLE-IOS: adrp	x8, __MergedGlobals_x@PAGE
+;CHECK-APPLE-IOS: add	x8, x8, __MergedGlobals_x@PAGEOFF
 ;CHECK-APPLE-IOS-NOT: adrp
   store i32 %a1, i32* @y, align 4
   store i32 %a2, i32* @z, align 4
@@ -41,12 +41,12 @@ define void @g1(i32 %a1, i32 %a2) {
 ;CHECK: z = .L_MergedGlobals+8
 ;CHECK: .size z, 4
 
-;CHECK-APPLE-IOS: .zerofill __DATA,__bss,l__MergedGlobals,12,3
+;CHECK-APPLE-IOS: .zerofill __DATA,__common,__MergedGlobals_x,12,3
 
 ;CHECK-APPLE-IOS: .globl	_x
-;CHECK-APPLE-IOS:  = l__MergedGlobals
+;CHECK-APPLE-IOS:  = __MergedGlobals_x
 ;CHECK-APPLE-IOS: .globl	_y
-;CHECK-APPLE-IOS: _y = l__MergedGlobals+4
+;CHECK-APPLE-IOS: _y = __MergedGlobals_x+4
 ;CHECK-APPLE-IOS: .globl	_z
-;CHECK-APPLE-IOS: _z = l__MergedGlobals+8
+;CHECK-APPLE-IOS: _z = __MergedGlobals_x+8
 ;CHECK-APPLE-IOS: .subsections_via_symbols

test/CodeGen/AArch64/global-merge-3.ll

@@ -7,11 +7,11 @@
 @z = internal global i32 1, align 4
 
 define void @f1(i32 %a1, i32 %a2, i32 %a3) {
-;CHECK-APPLE-IOS: adrp	x8, l__MergedGlobals@PAGE
+;CHECK-APPLE-IOS: adrp	x8, __MergedGlobals_x@PAGE
 ;CHECK-APPLE-IOS-NOT: adrp
-;CHECK-APPLE-IOS: add	x8, x8, l__MergedGlobals@PAGEOFF
-;CHECK-APPLE-IOS: adrp	x9, l__MergedGlobals.1@PAGE
-;CHECK-APPLE-IOS: add	x9, x9, l__MergedGlobals.1@PAGEOFF
+;CHECK-APPLE-IOS: add	x8, x8, __MergedGlobals_x@PAGEOFF
+;CHECK-APPLE-IOS: adrp	x9, __MergedGlobals_y@PAGE
+;CHECK-APPLE-IOS: add	x9, x9, __MergedGlobals_y@PAGEOFF
   %x3 = getelementptr inbounds [1000 x i32], [1000 x i32]* @x, i32 0, i64 3
   %y3 = getelementptr inbounds [1000 x i32], [1000 x i32]* @y, i32 0, i64 3
   store i32 %a1, i32* %x3, align 4
@@ -30,11 +30,11 @@ define void @f1(i32 %a1, i32 %a2, i32 %a3) {
 ;CHECK: .comm	.L_MergedGlobals.1,4000,16
 
 ;CHECK-APPLE-IOS: .p2align	4
-;CHECK-APPLE-IOS:  l__MergedGlobals:
+;CHECK-APPLE-IOS:  __MergedGlobals_x:
 ;CHECK-APPLE-IOS: .long 1
 ;CHECK-APPLE-IOS: .space	4000
 
-;CHECK-APPLE-IOS: .zerofill __DATA,__bss,l__MergedGlobals.1,4000,4
+;CHECK-APPLE-IOS: .zerofill __DATA,__common,__MergedGlobals_y,4000,4
 
 ;CHECK: z = .L_MergedGlobals
 ;CHECK:	.globl	x
@@ -44,8 +44,8 @@ define void @f1(i32 %a1, i32 %a2, i32 %a3) {
 ;CHECK: y = .L_MergedGlobals.1
 ;CHECK: .size y, 4000
 
-;CHECK-APPLE-IOS-NOT: _z = l__MergedGlobals
+;CHECK-APPLE-IOS-NOT: _z = __MergedGlobals_x
 ;CHECK-APPLE-IOS:.globl	_x
-;CHECK-APPLE-IOS: _x = l__MergedGlobals+4
+;CHECK-APPLE-IOS: _x = __MergedGlobals_x+4
 ;CHECK-APPLE-IOS:.globl	_y
-;CHECK-APPLE-IOS: _y = l__MergedGlobals.1
+;CHECK-APPLE-IOS: _y = __MergedGlobals_y

test/CodeGen/AArch64/global-merge-group-by-use.ll

@@ -13,7 +13,7 @@
 
 ; CHECK-LABEL: f1:
 define void @f1(i32 %a1, i32 %a2) #0 {
-; CHECK-NEXT: adrp x8, [[SET1:l__MergedGlobals.[0-9]*]]@PAGE
+; CHECK-NEXT: adrp x8, [[SET1:__MergedGlobals.[0-9]*]]@PAGE
 ; CHECK-NEXT: add x8, x8, [[SET1]]@PAGEOFF
 ; CHECK-NEXT: stp w0, w1, [x8]
 ; CHECK-NEXT: ret
@@ -28,7 +28,7 @@ define void @f1(i32 %a1, i32 %a2) #0 {
 
 ; CHECK-LABEL: f2:
 define void @f2(i32 %a1, i32 %a2, i32 %a3) #0 {
-; CHECK-NEXT: adrp x8, [[SET2:l__MergedGlobals.[0-9]*]]@PAGE
+; CHECK-NEXT: adrp x8, [[SET2:__MergedGlobals.[0-9]*]]@PAGE
 ; CHECK-NEXT: add x8, x8, [[SET2]]@PAGEOFF
 ; CHECK-NEXT: stp w0, w1, [x8]
 ; CHECK-NEXT: str w2, [x8, #8]
@@ -49,7 +49,7 @@ define void @f2(i32 %a1, i32 %a2, i32 %a3) #0 {
 ; CHECK-LABEL: f3:
 define void @f3(i32 %a1, i32 %a2) #0 {
 ; CHECK-NEXT: adrp x8, _m3@PAGE
-; CHECK-NEXT: adrp x9, [[SET3:l__MergedGlobals[0-9]*]]@PAGE
+; CHECK-NEXT: adrp x9, [[SET3:__MergedGlobals[0-9]*]]@PAGE
 ; CHECK-NEXT: str w0, [x8, _m3@PAGEOFF]
 ; CHECK-NEXT: str w1, [x9, [[SET3]]@PAGEOFF]
 ; CHECK-NEXT: ret

test/CodeGen/AArch64/global-merge-ignore-single-use-minsize.ll

@@ -11,7 +11,7 @@
 
 ; CHECK-LABEL: f1:
 define void @f1(i32 %a1, i32 %a2) minsize nounwind {
-; CHECK-NEXT: adrp x8, [[SET:l__MergedGlobals]]@PAGE
+; CHECK-NEXT: adrp x8, [[SET:__MergedGlobals]]@PAGE
 ; CHECK-NEXT: add x8, x8, [[SET]]@PAGEOFF
 ; CHECK-NEXT: stp w0, w1, [x8]
 ; CHECK-NEXT: ret

test/CodeGen/AArch64/global-merge-ignore-single-use.ll

@@ -11,7 +11,7 @@
 
 ; CHECK-LABEL: f1:
 define void @f1(i32 %a1, i32 %a2) #0 {
-; CHECK-NEXT: adrp x8, [[SET:l__MergedGlobals]]@PAGE
+; CHECK-NEXT: adrp x8, [[SET:__MergedGlobals]]@PAGE
 ; CHECK-NEXT: add x8, x8, [[SET]]@PAGEOFF
 ; CHECK-NEXT: stp w0, w1, [x8]
 ; CHECK-NEXT: ret

test/CodeGen/ARM/2011-06-29-MergeGlobalsAlign.ll

@@ -1,5 +1,5 @@
 ; RUN: llc < %s -mtriple=thumbv7-apple-darwin10 -arm-global-merge -global-merge-group-by-use=false | FileCheck %s
-; CHECK: .zerofill __DATA,__bss,l__MergedGlobals,16,2
+; CHECK: .zerofill __DATA,__bss,__MergedGlobals,16,2
 
 @prev = external global [0 x i16]
 @max_lazy_match = internal unnamed_addr global i32 0, align 4

test/CodeGen/ARM/global-merge-1.ll

@@ -11,16 +11,16 @@
 ; MERGE-NOT: .zerofill __DATA,__bss,_bar,20,2
 ; MERGE-NOT: .zerofill __DATA,__bss,_baz,20,2
 ; MERGE-NOT: .zerofill __DATA,__bss,_foo,20,2
-; MERGE: .zerofill __DATA,__bss,l__MergedGlobals,60,4
+; MERGE: .zerofill __DATA,__bss,__MergedGlobals,60,4
 ; MERGE-NOT: .zerofill __DATA,__bss,_bar,20,2
 ; MERGE-NOT: .zerofill __DATA,__bss,_baz,20,2
 ; MERGE-NOT: .zerofill __DATA,__bss,_foo,20,2
 
-; NO-MERGE-NOT: .zerofill __DATA,__bss,l__MergedGlobals,60,4
+; NO-MERGE-NOT: .zerofill __DATA,__bss,__MergedGlobals,60,4
 ; NO-MERGE: .zerofill __DATA,__bss,_bar,20,2
 ; NO-MERGE: .zerofill __DATA,__bss,_baz,20,2
 ; NO-MERGE: .zerofill __DATA,__bss,_foo,20,2
-; NO-MERGE-NOT: .zerofill __DATA,__bss,l__MergedGlobals,60,4
+; NO-MERGE-NOT: .zerofill __DATA,__bss,__MergedGlobals,60,4
 
 target datalayout = "e-p:32:32:32-i1:8:32-i8:8:32-i16:16:32-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:32:64-v128:32:128-a0:0:32-n32-S32"
 target triple = "thumbv7-apple-ios3.0.0"