Redo "Make global aliases have symbol size equal to their type"

r242520 was reverted in r244313 as the expected behaviour of the alias
attribute in C is that the alias has the same size as the aliasee. However
we can re-introduce adding the size on the alias when the aliasee does not,
from a source code or object perspective, exist as a discrete entity. This
happens when the aliasee is not a symbol, or when that symbol is private.

Differential Revision: http://reviews.llvm.org/D11943

llvm-svn: 244752

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -1184,6 +1184,20 @@ bool AsmPrinter::doFinalization(Module &M) {
 
     // Emit the directives as assignments aka .set:
     OutStreamer->EmitAssignment(Name, lowerConstant(Alias.getAliasee()));
+
+    // If the aliasee does not correspond to a symbol in the output, i.e. the
+    // alias is not of an object or the aliased object is private, then set the
+    // size of the alias symbol from the type of the alias. We don't do this in
+    // other situations as the alias and aliasee having differing types but same
+    // size may be intentional.
+    const GlobalObject *BaseObject = Alias.getBaseObject();
+    if (MAI->hasDotTypeDotSizeDirective() && Alias.getValueType()->isSized() &&
+        (!BaseObject || BaseObject->hasPrivateLinkage())) {
+      const DataLayout &DL = M.getDataLayout();
+      uint64_t Size = DL.getTypeAllocSize(Alias.getValueType());
+      OutStreamer->emitELFSize(cast<MCSymbolELF>(Name),
+                               MCConstantExpr::create(Size, OutContext));
+    }
   }
 
   GCModuleInfo *MI = getAnalysisIfAvailable<GCModuleInfo>();

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

@@ -33,10 +33,13 @@ define void @g1(i32 %a1, i32 %a2) {
 
 ;CHECK:	.globl	x
 ;CHECK: x = .L_MergedGlobals
+;CHECK: .size x, 4
 ;CHECK:	.globl	y
 ;CHECK: y = .L_MergedGlobals+4
+;CHECK: .size y, 4
 ;CHECK:	.globl	z
 ;CHECK: z = .L_MergedGlobals+8
+;CHECK: .size z, 4
 
 ;CHECK-APPLE-IOS: .zerofill __DATA,__bss,l__MergedGlobals,12,3
 

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

@@ -39,8 +39,10 @@ define void @f1(i32 %a1, i32 %a2, i32 %a3) {
 ;CHECK: z = .L_MergedGlobals
 ;CHECK:	.globl	x
 ;CHECK: x = .L_MergedGlobals+4
+;CHECK: .size x, 4000
 ;CHECK:	.globl	y
 ;CHECK: y = .L_MergedGlobals.1
+;CHECK: .size y, 4000
 
 ;CHECK-APPLE-IOS-NOT: _z = l__MergedGlobals
 ;CHECK-APPLE-IOS:.globl	_x

test/CodeGen/ARM/aliases.ll

@@ -2,19 +2,35 @@
 
 ; CHECK: .globl	test
 
+; CHECK: .Lstructvar:
+; CHECK: .size .Lstructvar, 8
+
 ; CHECK: .globl	foo1
 ; CHECK: foo1 = bar
+; CHECK-NOT: .size foo1
 
 ; CHECK: .globl	foo2
 ; CHECK: foo2 = bar
+; CHECK-NOT: .size foo2
 
 ; CHECK: .weak	bar_f
 ; CHECK: bar_f = foo_f
+; CHECK-NOT: .size bar_f
 
 ; CHECK: bar_i = bar
+; CHECK-NOT: .size bar_i
 
 ; CHECK: .globl	A
 ; CHECK: A = bar
+; CHECK-NOT: .size A
+
+; CHECK: .globl elem0
+; CHECK: elem0 = .Lstructvar
+; CHECK: .size elem0, 4
+
+; CHECK: .globl elem1
+; CHECK: elem1 = .Lstructvar+4
+; CHECK: .size elem1, 4
 
 @bar = global i32 42
 @foo1 = alias i32* @bar
@@ -31,6 +47,10 @@ define i32 @foo_f() {
 
 @A = alias bitcast (i32* @bar to i64*)
 
+@structvar = private global {i32, i32} {i32 1, i32 2}
+@elem0 = alias getelementptr({i32, i32}, {i32, i32}*  @structvar, i32 0, i32 0)
+@elem1 = alias getelementptr({i32, i32}, {i32, i32}*  @structvar, i32 0, i32 1)
+
 define i32 @test() {
 entry:
    %tmp = load i32, i32* @foo1

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

@@ -37,7 +37,10 @@ define void @g1(i32 %a1, i32 %a2) {
 
 ;CHECK-MERGE:	.globl	x
 ;CHECK-MERGE: x = .L_MergedGlobals
+;CHECK-MERGE: .size x, 4
 ;CHECK-MERGE:	.globl	y
 ;CHECK-MERGE: y = .L_MergedGlobals+4
+;CHECK-MERGE: .size y, 4
 ;CHECK-MERGE:	.globl	z
 ;CHECK-MERGE: z = .L_MergedGlobals+8
+;CHECK-MERGE: .size z, 4