[AsmPrinter] Change alignment of .stack_sizes from 1 to PointerSize

[MaskRay]

Summary

Fixes problem 1 of https://bugs.llvm.org/show_bug.cgi?id=36717

[grimar]

Seems the following comment https://bugs.llvm.org/show_bug.cgi?id=36717#c2 from @jhenderson was never answered.
Can you explain why it is a problem?

[MaskRay]

In D74815#1882132, @grimar wrote:

Seems the following comment https://bugs.llvm.org/show_bug.cgi?id=36717#c2 from @jhenderson was never answered.
Can you explain why it is a problem?

I was very late at my time when I was making the change. The size is encoded in uleb128, so............ the output section naturally contains unaligned entries. An alignment will be a bad idea.

A symbolic relocation referencing a local symbol is fine. If it references a global symbol, there could be problems like https://sourceware.org/bugzilla/show_bug.cgi?id=24896

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

void AsmPrinter::emitStackSizeSection(const MachineFunction &MF) {
   // Don't emit functions with dynamic stack allocations.
   if (FrameInfo.hasVarSizedObjects())
     return;
 
   OutStreamer->PushSection();
   OutStreamer->SwitchSection(StackSizeSection);
 
   const MCSymbol *FunctionSymbol = getFunctionBegin();
+  const unsigned PointerSize = getPointerSize();
   uint64_t StackSize = FrameInfo.getStackSize();
-  OutStreamer->emitSymbolValue(FunctionSymbol, TM.getProgramPointerSize());
+  emitAlignment(Align(PointerSize));
+  OutStreamer->emitSymbolValue(FunctionSymbol, PointerSize);
   OutStreamer->emitULEB128IntValue(StackSize);
 
   OutStreamer->PopSection();
 }
 
 static bool needFuncLabelsForEHOrDebugInfo(const MachineFunction &MF,
                                            MachineModuleInfo *MMI) {
   if (!MF.getLandingPads().empty() || MF.hasEHFunclets() || MMI->hasDebugInfo())

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

 ; RUN: llc < %s -mtriple=armv7-linux -stack-size-section | FileCheck %s
 
 ; CHECK-LABEL: func1:
 ; CHECK-NEXT: .Lfunc_begin0:
 ; CHECK: .section .stack_sizes,"o",%progbits,.text{{$}}
+; CHECK-NEXT: .p2align 2
 ; CHECK-NEXT: .long .Lfunc_begin0
 ; CHECK-NEXT: .byte 8
 define void @func1(i32, i32) #0 {
   alloca i32, align 4
   alloca i32, align 4
   ret void
 }
 
 ; CHECK-LABEL: func2:
 ; CHECK-NEXT: .Lfunc_begin1:
 ; CHECK: .section .stack_sizes,"o",%progbits,.text{{$}}
+; CHECK-NEXT: .p2align 2
 ; CHECK-NEXT: .long .Lfunc_begin1
 ; 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 = { "frame-pointer"="all" }

llvm/test/CodeGen/SystemZ/stack-size-section.ll

 ; RUN: llc < %s -mtriple=s390x-linux-gnu -stack-size-section | FileCheck %s
 
 ; CHECK-LABEL: func1:
 ; CHECK-NEXT: .Lfunc_begin0:
 ; CHECK: .section .stack_sizes,"o",@progbits,.text{{$}}
+; CHECK-NEXT: .p2align 3
 ; CHECK-NEXT: .quad .Lfunc_begin0
 ; CHECK-NEXT: .byte 0
 define void @func1(i32, i32) #0 {
   ret void
 }
 
 ; CHECK-LABEL: func2:
 ; CHECK-NEXT: .Lfunc_begin1:
 ; CHECK: .section .stack_sizes,"o",@progbits,.text{{$}}
+; CHECK-NEXT: .p2align 3
 ; CHECK-NEXT: .quad .Lfunc_begin1
 ; CHECK-NEXT: .ascii  "\250\001"
 define void @func2(i32, i32) #0 {
   alloca i32, align 4
   alloca i32, align 4
   ret void
 }
 
 ; CHECK-LABEL: func3:
 ; CHECK-NEXT: .Lfunc_begin2:
 ; CHECK: .section .stack_sizes,"o",@progbits,.text{{$}}
+; CHECK-NEXT: .p2align 3
 ; CHECK-NEXT: .quad .Lfunc_begin2
 ; CHECK-NEXT: .ascii  "\250\001"
 define void @func3() #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 = { "frame-pointer"="all" }

llvm/test/CodeGen/X86/stack-size-section.ll

 ; RUN: llc < %s -mtriple=x86_64-linux -stack-size-section | FileCheck %s
 
 ; CHECK-LABEL: func1:
 ; CHECK-NEXT: .Lfunc_begin0:
 ; CHECK: .section .stack_sizes,"o",@progbits,.text{{$}}
+; CHECK-NEXT: .p2align 3
 ; CHECK-NEXT: .quad .Lfunc_begin0
 ; CHECK-NEXT: .byte 8
 define void @func1(i32, i32) #0 {
   alloca i32, align 4
   alloca i32, align 4
   ret void
 }
 
 ; CHECK-LABEL: func2:
 ; CHECK-NEXT: .Lfunc_begin1:
 ; CHECK: .section .stack_sizes,"o",@progbits,.text{{$}}
+; CHECK-NEXT: .p2align 3
 ; CHECK-NEXT: .quad .Lfunc_begin1
 ; CHECK-NEXT: .byte 24
 define void @func2() #0 {
   alloca i32, align 4
   call void @func1(i32 1, i32 2)
   ret void
 }