[AIX][XCOFF] generate eh_info when vector registers are saved accordi…

…ng to the traceback table.

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

Reviewers: Jason Liu
Differential Revision: https://reviews.llvm.org/D103651

llvm/lib/CodeGen/AsmPrinter/AIXException.cpp

@@ -61,6 +61,9 @@ void AIXException::emitExceptionInfoTable(const MCSymbol *LSDA,
 }
 
 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;
 

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -203,6 +203,7 @@ class PPCAIXAsmPrinter : public PPCAsmPrinter {
   DenseMap<const GlobalObject *, SmallVector<const GlobalAlias *, 1>>
       GOAliasMap;
 
+  uint16_t getNumberOfVRSaved();
   void emitTracebackTable();
 
   SmallVector<const GlobalVariable *, 8> TOCDataGlobalVars;
@@ -1881,12 +1882,53 @@ void PPCAIXAsmPrinter::SetupMachineFunction(MachineFunction &MF) {
   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() {
@@ -2041,7 +2083,10 @@ void PPCAIXAsmPrinter::emitTracebackTable() {
   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;
 
@@ -2151,26 +2196,16 @@ void PPCAIXAsmPrinter::emitTracebackTable() {
 
   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) &
-              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;
-        }
+    if (NumOfVRSaved) {
+      // Number of VRs saved.
+      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;
     }
 
     // Set has_varargs.

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

@@ -69,7 +69,7 @@ entry:
 ; 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
@@ -80,4 +80,17 @@ entry:
 ; 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