MachineModuleInfo: Remove UsesMorestackAddr

This is x86 specific, and adds statefulness to
MachineModuleInfo. Instead of explicitly tracking this, infer if we
need to declare the symbol based on the reference previously inserted.

This produces a small change in the output due to the move from
AsmPrinter::doFinalization to X86's emitEndOfAsmFile. This will now be
moved relative to other end of file fields, which I'm assuming doesn't
matter (e.g. the __morestack_addr declaration is now after the
.note.GNU-split-stack part)

This also produces another small change in code if the module happened
to define/declare __morestack_addr, but I assume that's invalid and
doesn't really matter.

Author: arsenm

llvm/include/llvm/CodeGen/MachineModuleInfo.h

@@ -123,12 +123,6 @@ class MachineModuleInfo {
   /// point.  This is used to emit an undefined reference to _fltused.
   bool UsesMSVCFloatingPoint;
 
-  /// True if the module calls the __morestack function indirectly, as is
-  /// required under the large code model on x86. This is used to emit
-  /// a definition of a symbol, __morestack_addr, containing the address. See
-  /// comments in lib/Target/X86/X86FrameLowering.cpp for more details.
-  bool UsesMorestackAddr;
-
   /// Maps IR Functions to their corresponding MachineFunctions.
   DenseMap<const Function*, std::unique_ptr<MachineFunction>> MachineFunctions;
   /// Next unique number available for a MachineFunction.
@@ -195,14 +189,6 @@ class MachineModuleInfo {
 
   void setUsesMSVCFloatingPoint(bool b) { UsesMSVCFloatingPoint = b; }
 
-  bool usesMorestackAddr() const {
-    return UsesMorestackAddr;
-  }
-
-  void setUsesMorestackAddr(bool b) {
-    UsesMorestackAddr = b;
-  }
-
   /// Return the symbol to be used for the specified basic block when its
   /// address is taken.  This cannot be its normal LBB label because the block
   /// may be accessed outside its containing function.

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -1904,23 +1904,6 @@ bool AsmPrinter::doFinalization(Module &M) {
   // Emit bytes for llvm.commandline metadata.
   emitModuleCommandLines(M);
 
-  // Emit __morestack address if needed for indirect calls.
-  if (MMI->usesMorestackAddr()) {
-    Align Alignment(1);
-    MCSection *ReadOnlySection = getObjFileLowering().getSectionForConstant(
-        getDataLayout(), SectionKind::getReadOnly(),
-        /*C=*/nullptr, Alignment);
-    OutStreamer->SwitchSection(ReadOnlySection);
-
-    MCSymbol *AddrSymbol =
-        OutContext.getOrCreateSymbol(StringRef("__morestack_addr"));
-    OutStreamer->emitLabel(AddrSymbol);
-
-    unsigned PtrSize = MAI->getCodePointerSize();
-    OutStreamer->emitSymbolValue(GetExternalSymbolSymbol("__morestack"),
-                                 PtrSize);
-  }
-
   // Emit .note.GNU-split-stack and .note.GNU-no-split-stack sections if
   // split-stack is used.
   if (TM.getTargetTriple().isOSBinFormatELF() && HasSplitStack) {

llvm/lib/CodeGen/MachineModuleInfo.cpp

@@ -202,7 +202,7 @@ void MachineModuleInfo::initialize() {
   ObjFileMMI = nullptr;
   CurCallSite = 0;
   NextFnNum = 0;
-  UsesMSVCFloatingPoint = UsesMorestackAddr = false;
+  UsesMSVCFloatingPoint = false;
   AddrLabelSymbols = nullptr;
   DbgInfoAvailable = false;
 }
@@ -230,7 +230,6 @@ MachineModuleInfo::MachineModuleInfo(MachineModuleInfo &&MMI)
   ObjFileMMI = MMI.ObjFileMMI;
   CurCallSite = MMI.CurCallSite;
   UsesMSVCFloatingPoint = MMI.UsesMSVCFloatingPoint;
-  UsesMorestackAddr = MMI.UsesMorestackAddr;
   AddrLabelSymbols = MMI.AddrLabelSymbols;
   ExternalContext = MMI.ExternalContext;
   TheModule = MMI.TheModule;

llvm/lib/Target/X86/X86AsmPrinter.cpp

@@ -29,6 +29,7 @@
 #include "llvm/IR/Mangler.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
+#include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCCodeEmitter.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
@@ -803,6 +804,22 @@ void X86AsmPrinter::emitEndOfAsmFile(Module &M) {
     emitStackMaps(SM);
     FM.serializeToFaultMapSection();
   }
+
+  // Emit __morestack address if needed for indirect calls.
+  if (TT.getArch() == Triple::x86_64 && TM.getCodeModel() == CodeModel::Large) {
+    if (MCSymbol *AddrSymbol = OutContext.lookupSymbol("__morestack_addr")) {
+      Align Alignment(1);
+      MCSection *ReadOnlySection = getObjFileLowering().getSectionForConstant(
+          getDataLayout(), SectionKind::getReadOnly(),
+          /*C=*/nullptr, Alignment);
+      OutStreamer->SwitchSection(ReadOnlySection);
+      OutStreamer->emitLabel(AddrSymbol);
+
+      unsigned PtrSize = MAI->getCodePointerSize();
+      OutStreamer->emitSymbolValue(GetExternalSymbolSymbol("__morestack"),
+                                   PtrSize);
+    }
+  }
 }
 
 //===----------------------------------------------------------------------===//

llvm/lib/Target/X86/X86FrameLowering.cpp

@@ -3128,7 +3128,6 @@ void X86FrameLowering::adjustForSegmentedStacks(
         .addReg(0)
         .addExternalSymbol("__morestack_addr")
         .addReg(0);
-    MF.getMMI().setUsesMorestackAddr(true);
   } else {
     if (Is64Bit)
       BuildMI(allocMBB, DL, TII.get(X86::CALL64pcrel32))

llvm/test/CodeGen/X86/morestack-decl.ll

@@ -0,0 +1,10 @@
+; RUN: llc -mcpu=generic -mtriple=x86_64-linux -code-model=large < %s | FileCheck %s
+
+; Check what happens if we have an existing declaration of __morestack_addr
+
+; CHECK:	.section	".note.GNU-stack","",@progbits
+; CHECK-NEXT:	.section	.rodata,"a",@progbits
+; CHECK-NEXT: __morestack_addr:
+; CHECK-NEXT: .quad	__morestack
+
+declare void @__morestack_addr()

llvm/test/CodeGen/X86/segmented-stacks.ll

@@ -2123,7 +2123,10 @@ define i32 @test_nested_unused(i32 * nest %unused) #0 {
 
 attributes #0 = { "split-stack" }
 
-; X64-Linux-Large: .rodata
+; X64-Linux-Large: .section ".note.GNU-split-stack","",@progbits
+; X64-Linux-Large-NEXT: .section ".note.GNU-no-split-stack","",@progbits
+; X64-Linux-Large-NEXT: .section	".note.GNU-stack","",@progbits
+; X64-Linux-Large-NEXT: .rodata
 ; X64-Linux-Large-NEXT: __morestack_addr:
 ; X64-Linux-Large-NEXT: .quad	__morestack