[AIX][XCOFF] generate eh_info when vector registers are saved according to the traceback table.

[DiggerLin]

Summary

generate eh_info when vector registers are saved according to the traceback table.

struct eh_info_t {

unsigned version;       /* EH info version 0 */

#if defined(64BIT)

char _pad[4];           /* padding */

#endif

unsigned long lsda;     /* Pointer to Language Specific Data Area */
unsigned long personality; /* Pointer to the personality routine */

};

the value of lsda and personality is zero when the number of vector registers saved is large zero and there is not personality of the function

[DiggerLin]

fix a bug

[jasonliu]

llvm/include/llvm/CodeGen/AsmPrinter.h

755 ↗

(On Diff #349907)

I don't feel like this function belong in AsmPrinter.
This function feels more like a PPCFunctionInfo class function.
Admittedly, doing that means in AIXException.cpp, you would need to do an include like this: `#include ../../Target/PowerPC/PPCMachineFunctionInfo.h", which I don't see very often in the llvm source.
Not sure if this is an acceptable practice. @hubert.reinterpretcast any ideas?

The other way of doing this without that weird include in AIXException.cpp would be to move the content in AIXException.cpp to PPCAIXAsmPrinter instead. That way, you will definitely have access to everything you need in the PPCAIXAsmPrinter context.

Other than that, I am not sure if there is a better way on how to encasuplate what's needed for knowing if the vector register is save. i.e. The fundamental issue here is the knowledge of the PPC vector register is in lib/Target/PowerPC directory, so whenever you need to know that knowledge from another directory (and in case, lib/CodeGen/AsmPrinter/AIXException.cpp), it's hard to pass the information in.

[DiggerLin]

llvm/include/llvm/CodeGen/AsmPrinter.h

755 ↗

(On Diff #349907)

if we include the #include ../../Target/PowerPC/PPCMachineFunctionInfo.h in the AIXException.cpp , we have to implement the function getNumberOfVRSaved in file PPCMachineFunctionInfo.h , (not in the PPCMachineFunctionInfo.cpp) , otherwise it is link error when generate libLLVMAsmPrinter.a. implement a large function in PPCMachineFunctionInfo.h is not a good idea.

[sfertile]

llvm/include/llvm/CodeGen/AsmPrinter.h

755 ↗

(On Diff #349907)

Why make it a member function at all, instead incorporate looping over to see if any of the CSR VRs are used in 'ShouldEmitEHBlock', and loop over and count the number of CSR VRs inline (or as a static helper with a MachineFunction argument) in PPCAIXAsmPrinter.cpp.

[DiggerLin]

llvm/include/llvm/CodeGen/AsmPrinter.h

755 ↗

(On Diff #349907)

bool TargetLoweringObjectFileXCOFF::ShouldEmitEHBlock() is the directory of "llvm\lib\codegen" , it can not access the something like "PPC::V20" , which define in the headerfile of directory lib/Target/PowerPC" , not in the llvm/include directory

[DiggerLin]

address comment

[jasonliu]

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

2198 ↗

(On Diff #352235)

nit:

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

1885

I'm thinking if it's better to move this calculation into SetupMachineFunction.
And have a private data member (i.e. CurrentFnVRSavedNum) to record the result, so that we don't need to calculate it multiply times below.

1908

A comment above to explain why we want to emit exception info table in this condition would be useful.

[jasonliu]

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

2214 ↗

(On Diff #352235)

In order for CodeGen to link successful, we would need AsmPrinter, but AsmPrinter already requires the CodeGen component for linking.
This could be a circular dependency.

[DiggerLin]

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

1885

there are only two places using the function, and there is not a lot workload of the function, I am prefer to keep as current implement, If you strong require me to implement as your suggestion , I can do as your suggestion.

[DiggerLin]

address comment

[jasonliu]

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

1908–1909

clang-format the suggested comment.

I would also suggest to put a comment in AIXException::endFunction to indicate there is another place that would emit this eh info table structure. In case someone needs to update this structure, they would know they need to update in both places.

2088

nit

2199–2208

This variable could move to above line 2112, so that you only need to call it once in emitTracebackTable().

[DiggerLin]

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

1908–1909

thanks

[DiggerLin]

address comment

[jasonliu]

LGTM. Thanks!

llvm/lib/CodeGen/AsmPrinter/AIXException.cpp

Asm->OutStreamer->emitValue(MCSymbolRefExpr::create(LSDA, Asm->OutContext),
                               PointerSize);
 
   // Personality routine.
   Asm->OutStreamer->emitValue(MCSymbolRefExpr::create(PerSym, Asm->OutContext),
                               PointerSize);
 }
 
 void AIXException::endFunction(const MachineFunction *MF) {
+  // There is no easy way to access register information in `AIXException`
+  // class. when ShouldEmitEHBlock is false and VRs are saved, A dumy eh info
+  // table are emitted in PPCAIXAsmPrinter::emitFunctionBodyEnd.
   if (!TargetLoweringObjectFileXCOFF::ShouldEmitEHBlock(MF))
     return;
 
   const MCSymbol *LSDALabel = emitExceptionTable();
 
   const Function &F = MF->getFunction();
   assert(F.hasPersonalityFn() &&
          "Landingpads are presented, but no personality routine is found.");
   const GlobalValue *Per =
       dyn_cast<GlobalValue>(F.getPersonalityFn()->stripPointerCasts());
   const MCSymbol *PerSym = Asm->TM.getSymbol(Per);
 
   emitExceptionInfoTable(LSDALabel, PerSym);
 }
 
 } // End of namespace llvm

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

private:
   /// sinit/sterm function names.
   std::string FormatIndicatorAndUniqueModId;
 
   // Record a list of GlobalAlias associated with a GlobalObject.
   // This is used for AIX's extra-label-at-definition aliasing strategy.
   DenseMap<const GlobalObject *, SmallVector<const GlobalAlias *, 1>>
       GOAliasMap;
 
+  uint16_t getNumberOfVRSaved();
   void emitTracebackTable();
 
   SmallVector<const GlobalVariable *, 8> TOCDataGlobalVars;
 
   void emitGlobalVariableHelper(const GlobalVariable *);
 
 public:
   PPCAIXAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
MCSectionXCOFF *FnDescSec =
           &MF.getFunction(), TM));
   FnDescSec->setAlignment(Align(Subtarget->isPPC64() ? 8 : 4));
 
   CurrentFnDescSym = FnDescSec->getQualNameSymbol();
 
   return AsmPrinter::SetupMachineFunction(MF);
 }
 
+uint16_t PPCAIXAsmPrinter::getNumberOfVRSaved() {
+  // Calculate the number of VRs be saved.
+  // Vector registers 20 through 31 are marked as reserved and cannot be used
+  // in the default ABI.
+  const PPCSubtarget &Subtarget = MF->getSubtarget<PPCSubtarget>();
+  if (Subtarget.isAIXABI() && Subtarget.hasAltivec() &&
+      TM.getAIXExtendedAltivecABI()) {
+    const MachineRegisterInfo &MRI = MF->getRegInfo();
+    for (unsigned Reg = PPC::V20; Reg <= PPC::V31; ++Reg)
+      if (MRI.isPhysRegModified(Reg))
+        // Number of VRs saved.
+        return PPC::V31 - Reg + 1;
+  }
+  return 0;
+}
+
 void PPCAIXAsmPrinter::emitFunctionBodyEnd() {
 
   if (!TM.getXCOFFTracebackTable())
     return;
 
   emitTracebackTable();
+
+  // If ShouldEmitEHBlock returns true, then the eh info table
+  // will be emitted via `AIXException::endFunction`. Otherwise, we
+  // need to emit a dumy eh info table when VRs are saved. We could not
+  // consolidate these two places into one because there is no easy way
+  // to access register information in `AIXException` class.
+  if (!TargetLoweringObjectFileXCOFF::ShouldEmitEHBlock(MF) &&
+      (getNumberOfVRSaved() > 0)) {
+    // Emit dummy EH Info Table.
+    OutStreamer->SwitchSection(getObjFileLowering().getCompactUnwindSection());
+    MCSymbol *EHInfoLabel =
+        TargetLoweringObjectFileXCOFF::getEHInfoTableSymbol(MF);
+    OutStreamer->emitLabel(EHInfoLabel);
+
+    // Version number.
+    OutStreamer->emitInt32(0);
+
+    const DataLayout &DL = MMI->getModule()->getDataLayout();
+    const unsigned PointerSize = DL.getPointerSize();
+    // Add necessary paddings in 64 bit mode.
+    OutStreamer->emitValueToAlignment(PointerSize);
+
+    OutStreamer->emitIntValue(0, PointerSize);
+    OutStreamer->emitIntValue(0, PointerSize);
+  }
 }
 
 void PPCAIXAsmPrinter::emitTracebackTable() {
 
   // Create a symbol for the end of function.
   MCSymbol *FuncEnd = createTempSymbol(MF->getName());
   OutStreamer->emitLabel(FuncEnd);
 
if (MRI.isPhysRegUsed(Reg, /* SkipRegMaskTest */ true)) {
       // Has VMX instruction.
       HasVectorInst = true;
       break;
     }
 
   if (FI->hasVectorParms() || HasVectorInst)
     SecondHalfOfMandatoryField |= TracebackTable::HasVectorInfoMask;
 
-  bool ShouldEmitEHBlock = TargetLoweringObjectFileXCOFF::ShouldEmitEHBlock(MF);
+  uint16_t NumOfVRSaved = getNumberOfVRSaved();
+  bool ShouldEmitEHBlock =
+      TargetLoweringObjectFileXCOFF::ShouldEmitEHBlock(MF) || NumOfVRSaved > 0;
+
   if (ShouldEmitEHBlock)
     SecondHalfOfMandatoryField |= TracebackTable::HasExtensionTableMask;
 
   uint32_t GPRSaved = 0;
 
   // X13 is reserved under 64-bit environment.
   unsigned GPRBegin = Subtarget->isPPC64() ? PPC::X14 : PPC::R13;
   unsigned GPREnd = Subtarget->isPPC64() ? PPC::X31 : PPC::R31;
#define GENVALUECOMMENT(PrefixAndName, V, Field)                               \
   if (FirstHalfOfMandatoryField & TracebackTable::IsAllocaUsedMask) {
     uint8_t AllocReg = XCOFF::AllocRegNo;
     OutStreamer->AddComment("AllocaUsed");
     OutStreamer->emitIntValueInHex(AllocReg, sizeof(AllocReg));
   }
 
   if (SecondHalfOfMandatoryField & TracebackTable::HasVectorInfoMask) {
     uint16_t VRData = 0;
-    // Calculate the number of VRs be saved.
-    // Vector registers 20 through 31 are marked as reserved and cannot be used
-    // in the default ABI.
-    const PPCSubtarget &Subtarget = MF->getSubtarget<PPCSubtarget>();
-    if (Subtarget.isAIXABI() && Subtarget.hasAltivec() &&
-        TM.getAIXExtendedAltivecABI()) {
-      for (unsigned Reg = PPC::V20; Reg <= PPC::V31; ++Reg)
-        if (MRI.isPhysRegModified(Reg)) {
-          // Number of VRs saved.
-          VRData |=
-              ((PPC::V31 - Reg + 1) << TracebackTable::NumberOfVRSavedShift) &
+    if (NumOfVRSaved) {
+      VRData |= (NumOfVRSaved << TracebackTable::NumberOfVRSavedShift) &
                 TracebackTable::NumberOfVRSavedMask;
-          // This bit is supposed to set only when the special register
-          // VRSAVE is saved on stack.
-          // However, IBM XL compiler sets the bit when any vector registers
-          // are saved on the stack. We will follow XL's behavior on AIX
-          // so that we don't get surprise behavior change for C code.
-          VRData |= TracebackTable::IsVRSavedOnStackMask;
-          break;
-        }
     }
 
     // Set has_varargs.
     if (FI->getVarArgsFrameIndex())
       VRData |= TracebackTable::HasVarArgsMask;
 
     // Vector parameters number.
     unsigned VectorParmsNum = FI->getVectorParmsNum();

llvm/test/CodeGen/PowerPC/aix-emit-tracebacktable-clobber-register.ll

 ; COMMON-NEXT:  .byte   0x20                            # -IsGlobaLinkage, -IsOutOfLineEpilogOrPrologue
 ; COMMON-NEXT:                                         # +HasTraceBackTableOffset, -IsInternalProcedure
 ; COMMON-NEXT:                                         # -HasControlledStorage, -IsTOCless
 ; COMMON-NEXT:                                         # -IsFloatingPointPresent
 ; COMMON-NEXT:                                         # -IsFloatingPointOperationLogOrAbortEnabled
 ; COMMON-NEXT:  .byte   0x40                            # -IsInterruptHandler, +IsFunctionNamePresent, -IsAllocaUsed
 ; COMMON-NEXT:                                         # OnConditionDirective = 0, -IsCRSaved, -IsLRSaved
 ; COMMON-NEXT:  .byte   0x80                            # +IsBackChainStored, -IsFixup, NumOfFPRsSaved = 0
-; COMMON-NEXT:  .byte   0x80                            # +HasVectorInfo, -HasExtensionTable, NumOfGPRsSaved = 0
+; COMMON-NEXT:  .byte   0xc0                            # +HasVectorInfo, +HasExtensionTable, NumOfGPRsSaved = 0
 ; COMMON-NEXT:  .byte   0x00                            # NumberOfFixedParms = 0
 ; COMMON-NEXT:  .byte   0x01                            # NumberOfFPParms = 0, +HasParmsOnStack
 ; CHECK-ASM-NEXT:   .vbyte  4, L..foov0-.foov               # Function size
 ; CHECK-FUNC-NEXT:  .vbyte  4, L..foov0-.foov[PR]           # Function size
 ; COMMON-NEXT:  .vbyte  2, 0x0004                       # Function name len = 4
 ; COMMON-NEXT:  .byte   "foov"                          # Function Name 
 ; COMMON-NEXT:  .byte   0x12                            # NumOfVRsSaved = 4, +IsVRSavedOnStack, -HasVarArgs
 ; COMMON-NEXT:  .byte   0x01                            # NumOfVectorParams = 0, +HasVMXInstruction
 ; COMMON-NEXT:  .vbyte  4, 0x00000000                   # Vector Parameter type =
 ; COMMON-NEXT:  .vbyte  2, 0x0000                       # Padding 
+; COMMON-NEXT:  .byte   0x08                            # ExtensionTableFlag = TB_EH_INFO
+; COMMON-NEXT:  .align  2
+; COMMON-NEXT:  .vbyte  4, L..C2-TOC[TC0]               # EHInfo Table
+
+; COMMON:       .csect .eh_info_table[RW],2
+; COMMON-NEXT:__ehinfo.1:
+; COMMON-NEXT:  .vbyte  4, 0
+; COMMON-NEXT:  .align  2
+; COMMON-NEXT:  .vbyte  4, 0
+; COMMON-NEXT:  .vbyte  4, 0
 ; COMMON-NEXT:                                         # -- End function
+; COMMON:       .toc
+; COMMON:      L..C2:
+; COMMON-NEXT:  .tc __ehinfo.1[TC],__ehinfo.1