[MC] Fix -stack-size-section on ARM

[seaneveson]

Summary

Change symbol values in the stack size section from being 8 bytes, to being a target dependent size.

This simplifies reading the section for architectures with 32 bit symbols, and fixes an issue with an ARM target where the assembler didn't have a 64 bit data directive.

Thanks.

[MatzeB]

LGTM.

llvm/trunk/docs/CodeGenerator.rst

 implement an assembler for your target.
 
 Emitting function stack size information
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 A section containing metadata on function stack sizes will be emitted when
 ``TargetLoweringObjectFile::StackSizesSection`` is not null, and
 ``TargetOptions::EmitStackSizeSection`` is set (-stack-size-section). The
-section will contain an array of pairs of function symbol references (8 byte)
+section will contain an array of pairs of function symbol values (pointer size)
 and stack sizes (unsigned LEB128). The stack size values only include the space
 allocated in the function prologue. Functions with dynamic stack allocations are
 not included.
 
 VLIW Packetizer
 ---------------
 
 In a Very Long Instruction Word (VLIW) architecture, the compiler is responsible

llvm/trunk/docs/CommandGuide/llc.rst

 .. option:: -meabi=[default|gnu|4|5]
 
  Specify which EABI version should conform to.  Valid EABI versions are *gnu*,
  *4* and *5*.  Default value (*default*) depends on the triple.
 
 .. option:: -stack-size-section
 
  Emit the .stack_sizes section which contains stack size metadata. The section
- contains an array of pairs of function symbol references (8 byte) and stack
+ contains an array of pairs of function symbol values (pointer size) and stack
  sizes (unsigned LEB128). The stack size values only include the space allocated
  in the function prologue. Functions with dynamic stack allocations are not
  included.
 
 
 Tuning/Configuration Options
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

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

void AsmPrinter::emitStackSizeSection(const MachineFunction &MF) {
   if (FrameInfo.hasVarSizedObjects())
     return;
 
   OutStreamer->PushSection();
   OutStreamer->SwitchSection(StackSizeSection);
 
   const MCSymbol *FunctionSymbol = getSymbol(&MF.getFunction());
   uint64_t StackSize = FrameInfo.getStackSize();
-  OutStreamer->EmitValue(MCSymbolRefExpr::create(FunctionSymbol, OutContext),
-                         /* size = */ 8);
+  OutStreamer->EmitSymbolValue(FunctionSymbol, TM.getPointerSize());
   OutStreamer->EmitULEB128IntValue(StackSize);
 
   OutStreamer->PopSection();
 }
 
 static bool needFuncLabelsForEHOrDebugInfo(const MachineFunction &MF,
                                            MachineModuleInfo *MMI) {
   if (!MF.getLandingPads().empty() || MF.hasEHFunclets() || MMI->hasDebugInfo())

llvm/trunk/test/CodeGen/ARM/stack-size-section.ll

+; RUN: llc < %s -mtriple=armv7-linux -stack-size-section | FileCheck %s
+
+; CHECK-LABEL: func1:
+; CHECK: .section .stack_sizes,"",%progbits
+; CHECK-NEXT: .long func1
+; CHECK-NEXT: .byte 8
+define void @func1(i32, i32) #0 {
+  alloca i32, align 4
+  alloca i32, align 4
+  ret void
+}
+
+; CHECK-LABEL: func2:
+; CHECK: .section .stack_sizes,"",%progbits
+; CHECK-NEXT: .long func2
+; CHECK-NEXT: .byte 16
+define void @func2() #0 {
+  alloca i32, align 4
+  call void @func1(i32 1, i32 2)
+  ret void
+}
+
+; CHECK-LABEL: dynalloc:
+; CHECK-NOT: .section .stack_sizes
+define void @dynalloc(i32 %N) #0 {
+  alloca i32, i32 %N
+  ret void
+}
+
+attributes #0 = { "no-frame-pointer-elim"="true" }