Allow the use of an alternate symbol for calculating a function's size.

The standard function epilog includes a .size directive, but ppc64 uses
an alternate local symbol to tag the actual start of each function.

Until recently, binutils accepted the .size directive as:
 .size	test1, .Ltmp0-test1
however, using this directive with recent binutils will result in the error:
 .size expression for XXX does not evaluate to a constant
so we must use the label which actually tags the start of the function.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151200 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/AsmPrinter.h

@@ -88,6 +88,11 @@ namespace llvm {
     ///
     MCSymbol *CurrentFnSym;
 
+    /// The symbol used to represent the start of the current function for the
+    /// purpose of calculating its size (e.g. using the .size directive). By
+    /// default, this is equal to CurrentFnSym.
+    MCSymbol *CurrentFnSymForSize;
+
   private:
     // GCMetadataPrinters - The garbage collection metadata printer table.
     void *GCMetadataPrinters;  // Really a DenseMap.

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -100,6 +100,7 @@ AsmPrinter::AsmPrinter(TargetMachine &tm, MCStreamer &Streamer)
     OutStreamer(Streamer),
     LastMI(0), LastFn(0), Counter(~0U), SetCounter(0) {
   DD = 0; DE = 0; MMI = 0; LI = 0;
+  CurrentFnSym = CurrentFnSymForSize = 0;
   GCMetadataPrinters = 0;
   VerboseAsm = Streamer.isVerboseAsm();
 }
@@ -761,7 +762,8 @@ void AsmPrinter::EmitFunctionBody() {
 
     const MCExpr *SizeExp =
       MCBinaryExpr::CreateSub(MCSymbolRefExpr::Create(FnEndLabel, OutContext),
-                              MCSymbolRefExpr::Create(CurrentFnSym, OutContext),
+                              MCSymbolRefExpr::Create(CurrentFnSymForSize,
+                                                      OutContext),
                               OutContext);
     OutStreamer.EmitELFSize(CurrentFnSym, SizeExp);
   }
@@ -951,6 +953,7 @@ void AsmPrinter::SetupMachineFunction(MachineFunction &MF) {
   this->MF = &MF;
   // Get the function symbol.
   CurrentFnSym = Mang->getSymbol(MF.getFunction());
+  CurrentFnSymForSize = CurrentFnSym;
 
   if (isVerbose())
     LI = &getAnalysis<MachineLoopInfo>();

lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -398,7 +398,11 @@ void PPCLinuxAsmPrinter::EmitFunctionEntryLabel() {
   OutStreamer.EmitRawText("\t.quad .L." + Twine(CurrentFnSym->getName()) +
                           ",.TOC.@tocbase");
   OutStreamer.EmitRawText(StringRef("\t.previous"));
-  OutStreamer.EmitRawText(".L." + Twine(CurrentFnSym->getName()) + ":");
+
+  MCSymbol *RealFnSym = OutContext.GetOrCreateSymbol(
+                          ".L." + Twine(CurrentFnSym->getName()));
+  OutStreamer.EmitLabel(RealFnSym);
+  CurrentFnSymForSize = RealFnSym;
 }
 
 

test/CodeGen/PowerPC/ppc64-linux-func-size.ll

@@ -0,0 +1,18 @@
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=g5 | FileCheck %s
+
+; CHECK: test1:
+; CHECK-NEXT:	.quad .L.test1,.TOC.@tocbase
+; CHECK-NEXT:	.previous
+; CHECK-NEXT: .L.test1:
+
+define i32 @test1(i32 %a) nounwind {
+entry:
+  ret i32 %a
+}
+
+; Until recently, binutils accepted the .size directive as:
+;  .size	test1, .Ltmp0-test1
+; however, using this directive with recent binutils will result in the error:
+;  .size expression for XXX does not evaluate to a constant
+; so we must use the label which actually tags the start of the function.
+; CHECK: .size	test1, .Ltmp0-.L.test1