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

[john.brawn]

Summary

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.

[• rafael]

This also needs a negative test showing when .size is *not* printed.

It would also be nice to add a test to clang with both -emit-llvm and -S. This is one of the special situations where I think an integration test makes sense. If we change how we represent this we will still want to make sure clang is not printing extra .size directives.

Thanks!

[john.brawn]

Make the test check that the size directive is not emitted when we expect it to not be emitted.

[john.brawn]

In D11943#221709, @rafael wrote:

It would also be nice to add a test to clang with both -emit-llvm and -S. This is one of the special situations where I think an integration test makes sense. If we change how we represent this we will still want to make sure clang is not printing extra .size directives.

http://reviews.llvm.org/D11980

[• rafael]

LGTM

llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

else if (Alias.hasWeakLinkage() || Alias.hasLinkOnceLinkage())
       OutStreamer->EmitSymbolAttribute(Name, MCSA_WeakReference);
     else
       assert(Alias.hasLocalLinkage() && "Invalid alias linkage");
 
     EmitVisibility(Name, Alias.getVisibility());
 
     // 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>();
   assert(MI && "AsmPrinter didn't require GCModuleInfo?");
   for (GCModuleInfo::iterator I = MI->end(), E = MI->begin(); I != E; )
     if (GCMetadataPrinter *MP = GetOrCreateGCPrinter(**--I))
       MP->finishAssembly(M, *MI, *this);
 

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

 }
 
 ;CHECK: .type .L_MergedGlobals,@object // @_MergedGlobals
 ;CHECK: .local  .L_MergedGlobals
 ;CHECK: .comm .L_MergedGlobals,12,8
 
 ;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
 
 ;CHECK-APPLE-IOS: .globl  _x
 ;CHECK-APPLE-IOS:  = l__MergedGlobals
 ;CHECK-APPLE-IOS: .globl  _y
 ;CHECK-APPLE-IOS: _y = l__MergedGlobals+4
 ;CHECK-APPLE-IOS: .globl  _z
 ;CHECK-APPLE-IOS: _z = l__MergedGlobals+8
 ;CHECK-APPLE-IOS: .subsections_via_symbols

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

 ;CHECK-APPLE-IOS: .long 1
 ;CHECK-APPLE-IOS: .space  4000
 
 ;CHECK-APPLE-IOS: .zerofill __DATA,__bss,l__MergedGlobals.1,4000,4
 
 ;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
 ;CHECK-APPLE-IOS: _x = l__MergedGlobals+4
 ;CHECK-APPLE-IOS:.globl _y
 ;CHECK-APPLE-IOS: _y = l__MergedGlobals.1

llvm/trunk/test/CodeGen/ARM/aliases.ll

 ; RUN: llc < %s -mtriple=arm-linux-gnueabi | FileCheck %s
 
 ; 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
 @foo2 = alias i32* @bar
 
 %FunTy = type i32()
 
 define i32 @foo_f() {
   ret i32 0
 }
 @bar_f = weak alias %FunTy* @foo_f
 
 @bar_i = internal alias i32* @bar
 
 @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
    %tmp1 = load i32, i32* @foo2
    %tmp0 = load i32, i32* @bar_i
    %tmp2 = call i32 @foo_f()
    %tmp3 = add i32 %tmp, %tmp2
    %tmp4 = call i32 @bar_f()
    %tmp5 = add i32 %tmp3, %tmp4
    %tmp6 = add i32 %tmp1, %tmp5
    %tmp7 = add i32 %tmp6, %tmp0
    ret i32 %tmp7
 }

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

 ;CHECK-NO-MERGE-NOT: .globl .L_MergedGlobals
 
 ;CHECK-MERGE: .type .L_MergedGlobals,%object
 ;CHECK-MERGE: .local  .L_MergedGlobals
 ;CHECK-MERGE: .comm .L_MergedGlobals,12,4
 
 ;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