This patch is needed to make c++ exceptions work for mips16.

Mips16 is really a processor decoding mode (ala thumb 1) and in the same
program, mips16 and mips32 functions can exist and can call each other.

If a jal type instruction encounters an address with the lower bit set, then
the processor switches to mips16 mode (if it is not already in it). If the
lower bit is not set, then it switches to mips32 mode.

The linker knows which functions are mips16 and which are mips32.
When relocation is performed on code labels, this lower order bit is
set if the code label is a mips16 code label.

In general this works just fine, however when creating exception handling
tables and dwarf, there are cases where you don't want this lower order
bit added in.

This has been traditionally distinguished in gas assembly source by using a
different syntax for the label.

lab1:      ; this will cause the lower order bit to be added
lab2=.     ; this will not cause the lower order bit to be added

In some cases, it does not matter because in dwarf and debug tables
the difference of two labels is used and in that case the lower order
bits subtract each other out.

To fix this, I have added to mcstreamer the notion of a debuglabel.
The default is for label and debug label to be the same. So calling
EmitLabel and EmitDebugLabel produce the same result.

For various reasons, there is only one set of labels that needs to be
modified for the mips exceptions to work. These are the "$eh_func_beginXXX" 
labels.

Mips overrides the debug label suffix from ":" to "=." .

This initial patch fixes exceptions. More changes most likely
will be needed to DwarfCFException to make all of this work
for actual debugging. These changes will be to emit debug labels in some
places where a simple label is emitted now.

Some historical discussion on this from gcc can be found at:
http://gcc.gnu.org/ml/gcc-patches/2008-08/msg00623.html
http://gcc.gnu.org/ml/gcc-patches/2008-11/msg01273.html 



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170279 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCAsmInfo.h

@@ -102,6 +102,9 @@ namespace llvm {
     /// LabelSuffix - This is appended to emitted labels.
     const char *LabelSuffix;                 // Defaults to ":"
 
+    /// LabelSuffix - This is appended to emitted labels.
+    const char *DebugLabelSuffix;                 // Defaults to ":"
+
     /// GlobalPrefix - If this is set to a non-empty string, it is prepended
     /// onto all global symbols.  This is often used for "_" or ".".
     const char *GlobalPrefix;                // Defaults to ""
@@ -426,6 +429,11 @@ namespace llvm {
     const char *getLabelSuffix() const {
       return LabelSuffix;
     }
+
+    const char *getDebugLabelSuffix() const {
+      return DebugLabelSuffix;
+    }
+
     const char *getGlobalPrefix() const {
       return GlobalPrefix;
     }

include/llvm/MC/MCELFStreamer.h

@@ -47,6 +47,7 @@ public:
   virtual void InitSections();
   virtual void ChangeSection(const MCSection *Section);
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
   virtual void EmitThumbFunc(MCSymbol *Func);
   virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);

include/llvm/MC/MCObjectStreamer.h

@@ -69,6 +69,7 @@ public:
   /// @{
 
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
   virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
   virtual void EmitValueImpl(const MCExpr *Value, unsigned Size,
                              unsigned AddrSpace);

include/llvm/MC/MCStreamer.h

@@ -244,6 +244,8 @@ namespace llvm {
     /// used in an assignment.
     virtual void EmitLabel(MCSymbol *Symbol);
 
+    virtual void EmitDebugLabel(MCSymbol *Symbol);
+
     virtual void EmitEHSymAttributes(const MCSymbol *Symbol,
                                      MCSymbol *EHSymbol);
 

lib/CodeGen/AsmPrinter/DwarfCFIException.cpp

@@ -122,8 +122,9 @@ void DwarfCFIException::BeginFunction(const MachineFunction *MF) {
   const MCSymbol *Sym = TLOF.getCFIPersonalitySymbol(Per, Asm->Mang, MMI);
   Asm->OutStreamer.EmitCFIPersonality(Sym, PerEncoding);
 
-  Asm->OutStreamer.EmitLabel(Asm->GetTempSymbol("eh_func_begin",
-                                                Asm->getFunctionNumber()));
+  Asm->OutStreamer.EmitDebugLabel
+    (Asm->GetTempSymbol("eh_func_begin",
+                        Asm->getFunctionNumber()));
 
   // Provide LSDA information.
   if (!shouldEmitLSDA)

lib/MC/MCAsmInfo.cpp

@@ -37,6 +37,7 @@ MCAsmInfo::MCAsmInfo() {
   CommentColumn = 40;
   CommentString = "#";
   LabelSuffix = ":";
+  DebugLabelSuffix = ":";
   GlobalPrefix = "";
   PrivateGlobalPrefix = ".";
   LinkerPrivateGlobalPrefix = "";

lib/MC/MCAsmStreamer.cpp

@@ -135,6 +135,8 @@ public:
   }
 
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
+
   virtual void EmitEHSymAttributes(const MCSymbol *Symbol,
                                    MCSymbol *EHSymbol);
   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
@@ -345,6 +347,14 @@ void MCAsmStreamer::EmitLabel(MCSymbol *Symbol) {
   EmitEOL();
 }
 
+void MCAsmStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
+  MCStreamer::EmitDebugLabel(Symbol);
+
+  OS << *Symbol << MAI.getDebugLabelSuffix();
+  EmitEOL();
+}
+
 void MCAsmStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
   switch (Flag) {
   case MCAF_SyntaxUnified:         OS << "\t.syntax unified"; break;

lib/MC/MCELFStreamer.cpp

@@ -86,6 +86,10 @@ void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
     MCELF::SetType(SD, ELF::STT_TLS);
 }
 
+void MCELFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  EmitLabel(Symbol);
+}
+
 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
   switch (Flag) {
   case MCAF_SyntaxUnified: return; // no-op here.

lib/MC/MCMachOStreamer.cpp

@@ -43,6 +43,7 @@ public:
 
   virtual void InitSections();
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
   virtual void EmitEHSymAttributes(const MCSymbol *Symbol,
                                    MCSymbol *EHSymbol);
   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
@@ -130,6 +131,9 @@ void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
   SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);
 }
 
+void MCMachOStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  EmitLabel(Symbol);
+}
 void MCMachOStreamer::EmitDataRegion(DataRegionData::KindTy Kind) {
   if (!getAssembler().getBackend().hasDataInCodeSupport())
     return;

lib/MC/MCNullStreamer.cpp

@@ -35,7 +35,9 @@ namespace {
       assert(getCurrentSection() && "Cannot emit before setting section!");
       Symbol->setSection(*getCurrentSection());
     }
-
+    virtual void EmitDebugLabel(MCSymbol *Symbol) {
+      EmitLabel(Symbol);
+    }
     virtual void EmitAssemblerFlag(MCAssemblerFlag Flag) {}
     virtual void EmitThumbFunc(MCSymbol *Func) {}
 

lib/MC/MCObjectStreamer.cpp

@@ -134,6 +134,10 @@ void MCObjectStreamer::EmitLabel(MCSymbol *Symbol) {
   SD.setOffset(F->getContents().size());
 }
 
+void MCObjectStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  EmitLabel(Symbol);
+}
+
 void MCObjectStreamer::EmitULEB128Value(const MCExpr *Value) {
   int64_t IntValue;
   if (Value->EvaluateAsAbsolute(IntValue, getAssembler())) {

lib/MC/MCPureStreamer.cpp

@@ -37,6 +37,7 @@ public:
 
   virtual void InitSections();
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
   virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
                             uint64_t Size = 0, unsigned ByteAlignment = 0);
   virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
@@ -134,6 +135,7 @@ void MCPureStreamer::EmitLabel(MCSymbol *Symbol) {
   SD.setOffset(F->getContents().size());
 }
 
+
 void MCPureStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
                                   uint64_t Size, unsigned ByteAlignment) {
   report_fatal_error("not yet implemented in pure streamer");

lib/MC/MCStreamer.cpp

@@ -195,6 +195,13 @@ void MCStreamer::EmitLabel(MCSymbol *Symbol) {
   LastSymbol = Symbol;
 }
 
+void MCStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  assert(!Symbol->isVariable() && "Cannot emit a variable symbol!");
+  assert(getCurrentSection() && "Cannot emit before setting section!");
+  Symbol->setSection(*getCurrentSection());
+  LastSymbol = Symbol;
+}
+
 void MCStreamer::EmitCompactUnwindEncoding(uint32_t CompactUnwindEncoding) {
   EnsureValidFrame();
   MCDwarfFrameInfo *CurFrame = getCurrentFrameInfo();

lib/MC/WinCOFFStreamer.cpp

@@ -51,6 +51,7 @@ public:
 
   virtual void InitSections();
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
   virtual void EmitThumbFunc(MCSymbol *Func);
   virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
@@ -176,6 +177,9 @@ void WinCOFFStreamer::EmitLabel(MCSymbol *Symbol) {
   MCObjectStreamer::EmitLabel(Symbol);
 }
 
+void WinCOFFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  EmitLabel(Symbol);
+}
 void WinCOFFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
   llvm_unreachable("not implemented");
 }

lib/Target/Mips/MCTargetDesc/MipsMCAsmInfo.cpp

@@ -34,7 +34,7 @@ MipsMCAsmInfo::MipsMCAsmInfo(const Target &T, StringRef TT) {
   GPRel32Directive            = "\t.gpword\t";
   GPRel64Directive            = "\t.gpdword\t";
   WeakRefDirective            = "\t.weak\t";
-
+  DebugLabelSuffix            = "=.";
   SupportsDebugInformation = true;
   ExceptionsType = ExceptionHandling::DwarfCFI;
   HasLEB128 = true;

test/CodeGen/Mips/mips16ex.ll

@@ -0,0 +1,87 @@
+; RUN: llc  -march=mipsel -mcpu=mips16 -relocation-model=pic -O3 < %s | FileCheck %s -check-prefix=16
+
+;16: $eh_func_begin0=.
+@.str = private unnamed_addr constant [7 x i8] c"hello\0A\00", align 1
+@_ZTIi = external constant i8*
+@.str1 = private unnamed_addr constant [15 x i8] c"exception %i \0A\00", align 1
+
+define i32 @main() {
+entry:
+  %retval = alloca i32, align 4
+  %exn.slot = alloca i8*
+  %ehselector.slot = alloca i32
+  %e = alloca i32, align 4
+  store i32 0, i32* %retval
+  %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([7 x i8]* @.str, i32 0, i32 0))
+  %exception = call i8* @__cxa_allocate_exception(i32 4) nounwind
+  %0 = bitcast i8* %exception to i32*
+  store i32 20, i32* %0
+  invoke void @__cxa_throw(i8* %exception, i8* bitcast (i8** @_ZTIi to i8*), i8* null) noreturn
+          to label %unreachable unwind label %lpad
+
+lpad:                                             ; preds = %entry
+  %1 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*)
+          catch i8* bitcast (i8** @_ZTIi to i8*)
+  %2 = extractvalue { i8*, i32 } %1, 0
+  store i8* %2, i8** %exn.slot
+  %3 = extractvalue { i8*, i32 } %1, 1
+  store i32 %3, i32* %ehselector.slot
+  br label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %lpad
+  %sel = load i32* %ehselector.slot
+  %4 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*)) nounwind
+  %matches = icmp eq i32 %sel, %4
+  br i1 %matches, label %catch, label %eh.resume
+
+catch:                                            ; preds = %catch.dispatch
+  %exn = load i8** %exn.slot
+  %5 = call i8* @__cxa_begin_catch(i8* %exn) nounwind
+  %6 = bitcast i8* %5 to i32*
+  %exn.scalar = load i32* %6
+  store i32 %exn.scalar, i32* %e, align 4
+  %7 = load i32* %e, align 4
+  %call2 = invoke i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([15 x i8]* @.str1, i32 0, i32 0), i32 %7)
+          to label %invoke.cont unwind label %lpad1
+
+invoke.cont:                                      ; preds = %catch
+  call void @__cxa_end_catch() nounwind
+  br label %try.cont
+
+try.cont:                                         ; preds = %invoke.cont
+  ret i32 0
+
+lpad1:                                            ; preds = %catch
+  %8 = landingpad { i8*, i32 } personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*)
+          cleanup
+  %9 = extractvalue { i8*, i32 } %8, 0
+  store i8* %9, i8** %exn.slot
+  %10 = extractvalue { i8*, i32 } %8, 1
+  store i32 %10, i32* %ehselector.slot
+  call void @__cxa_end_catch() nounwind
+  br label %eh.resume
+
+eh.resume:                                        ; preds = %lpad1, %catch.dispatch
+  %exn3 = load i8** %exn.slot
+  %sel4 = load i32* %ehselector.slot
+  %lpad.val = insertvalue { i8*, i32 } undef, i8* %exn3, 0
+  %lpad.val5 = insertvalue { i8*, i32 } %lpad.val, i32 %sel4, 1
+  resume { i8*, i32 } %lpad.val5
+
+unreachable:                                      ; preds = %entry
+  unreachable
+}
+
+declare i32 @printf(i8*, ...)
+
+declare i8* @__cxa_allocate_exception(i32)
+
+declare i32 @__gxx_personality_v0(...)
+
+declare void @__cxa_throw(i8*, i8*, i8*)
+
+declare i32 @llvm.eh.typeid.for(i8*) nounwind readnone
+
+declare i8* @__cxa_begin_catch(i8*)
+
+declare void @__cxa_end_catch()

tools/lto/LTOModule.cpp

@@ -745,6 +745,9 @@ namespace {
       Symbol->setSection(*getCurrentSection());
       markDefined(*Symbol);
     }
+    virtual void EmitDebugLabel(MCSymbol *Symbol) {
+      EmitLabel(Symbol);
+    }
     virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
       // FIXME: should we handle aliases?
       markDefined(*Symbol);