[PowerPC][AIX] Set the HasAlloca flag in the AIX Traceback Table only if R31 is used as a frame pointer

[ZarkoCA]

Summary

After c063946476e083a9a0c5bd397337d1ece4742ec6 usage of R31 doesn't necessarily mean
that alloca is used. The TracebackTable::IsAllocaUsedMask flag should be set only
when R31 is used as a frame pointer.

On AIX the `function calls alloca' bit seems to be set whenever R31 is
set up as a frame pointer, even when there is no alloca call.

[lkail]

Is the AllocaUsed bit indicating LLVM instruction alloca is used? If so, I'm assuming this patches refers to dynamic alloca, since r31 is used under this condition. There is a flag in MachineFrameInfo::hasVarSizedObjects for dynamic alloca. There are some other cases also using r31 as frame pointer, so use r31 here might be not accurate.

[ZarkoCA]

In D108141#2948615, @lkail wrote:

Is the AllocaUsed bit indicating LLVM instruction alloca is used? If so, I'm assuming this patches refers to dynamic alloca, since r31 is used under this condition. There is a flag in MachineFrameInfo::hasVarSizedObjects for dynamic alloca. There are some other cases also using r31 as frame pointer, so use r31 here might be not accurate.

Yes, that's a good suggestion howeever, according to the AIX convention:

The `function calls alloca' bit seems to be set whenever reg 31 is
set up as a frame pointer, even when there is no alloca call.

And this is why we have this implementation. As per your good offline suggestion I will also edit the description of the patch to make this clear.

[lkail]

LGTM, thanks.

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

#define GENVALUECOMMENT(PrefixAndName, V, Field)                               \
   EmitComment();
 
   OutStreamer->emitIntValueInHexWithPadding(
       (FirstHalfOfMandatoryField & 0x0000ff00) >> 8, 1);
 
   // Set the 4th byte of the mandatory field.
   FirstHalfOfMandatoryField |= TracebackTable::IsFunctionNamePresentMask;
 
-  static_assert(XCOFF::AllocRegNo == 31, "Unexpected register usage!");
-  if (MRI.isPhysRegUsed(Subtarget->isPPC64() ? PPC::X31 : PPC::R31,
-                        /* SkipRegMaskTest */ true))
+  const PPCRegisterInfo *RegInfo =
+      static_cast<const PPCRegisterInfo *>(Subtarget->getRegisterInfo());
+  Register FrameReg = RegInfo->getFrameRegister(*MF);
+  if (FrameReg == (Subtarget->isPPC64() ? PPC::X31 : PPC::R31))
     FirstHalfOfMandatoryField |= TracebackTable::IsAllocaUsedMask;
 
   const SmallVectorImpl<Register> &MustSaveCRs = FI->getMustSaveCRs();
   if (!MustSaveCRs.empty())
     FirstHalfOfMandatoryField |= TracebackTable::IsCRSavedMask;
 
   if (FI->mustSaveLR())
     FirstHalfOfMandatoryField |= TracebackTable::IsLRSavedMask;

llvm/test/CodeGen/PowerPC/aix-alloca-r31.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff -mcpu=pwr4 \
+; RUN:     -mattr=+altivec -vec-extabi -xcoff-traceback-table=true < %s | \
+; RUN:   FileCheck --check-prefix=CHECK-ASM32 %s
+
+; RUN: llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff -mcpu=pwr4 \
+; RUN:     -mattr=+altivec -vec-extabi -xcoff-traceback-table=true < %s | \
+; RUN:   FileCheck --check-prefix=CHECK-ASM64 %s
+
+@var = local_unnamed_addr global i32 0
+
+define i32 @varalloca() local_unnamed_addr {
+; CHECK-ASM32-LABEL: varalloca:
+; CHECK-ASM32:       # %bb.0: # %entry
+; CHECK-ASM32-NEXT:    stw 31, -4(1)
+; CHECK-ASM32-NEXT:    stwu 1, -48(1)
+; CHECK-ASM32-NEXT:    lwz 3, L..C0(2) # @var
+; CHECK-ASM32-NEXT:    mr 31, 1
+; CHECK-ASM32-NEXT:    addi 4, 31, 48
+; CHECK-ASM32-NEXT:    lwz 3, 0(3)
+; CHECK-ASM32-NEXT:    addi 3, 3, 15
+; CHECK-ASM32-NEXT:    rlwinm 3, 3, 0, 0, 27
+; CHECK-ASM32-NEXT:    neg 3, 3
+; CHECK-ASM32-NEXT:    stwux 4, 1, 3
+; CHECK-ASM32-NEXT:    addi 3, 1, 32
+; CHECK-ASM32-NEXT:    lwz 3, 0(3)
+; CHECK-ASM32-NEXT:    lwz 1, 0(1)
+; CHECK-ASM32-NEXT:    lwz 31, -4(1)
+; CHECK-ASM32-NEXT:    blr
+; CHECK-ASM32-NEXT:    L..varalloca0:
+; CHECK-ASM32-NEXT:     .vbyte  4, 0x00000000                   # Traceback table begin
+; CHECK-ASM32-NEXT:     .byte 0x00                            # Version = 0
+; CHECK-ASM32-NEXT:     .byte 0x09                            # Language = CPlusPlus
+; CHECK-ASM32-NEXT:     .byte 0x20                            # -IsGlobaLinkage, -IsOutOfLineEpilogOrPrologue
+; CHECK-ASM32-NEXT:                                            # +HasTraceBackTableOffset, -IsInternalProcedure
+; CHECK-ASM32-NEXT:                                            # -HasControlledStorage, -IsTOCless
+; CHECK-ASM32-NEXT:                                            # -IsFloatingPointPresent
+; CHECK-ASM32-NEXT:                                            # -IsFloatingPointOperationLogOrAbortEnabled
+; CHECK-ASM32-NEXT:     .byte 0x60                            # -IsInterruptHandler, +IsFunctionNamePresent, +IsAllocaUsed
+; CHECK-ASM32-NEXT:                                            # OnConditionDirective = 0, -IsCRSaved, -IsLRSaved
+; CHECK-ASM32-NEXT:     .byte 0x80                            # +IsBackChainStored, -IsFixup, NumOfFPRsSaved = 0
+; CHECK-ASM32-NEXT:     .byte 0x01                            # -HasExtensionTable, -HasVectorInfo, NumOfGPRsSaved = 1
+; CHECK-ASM32-NEXT:     .byte 0x00                            # NumberOfFixedParms = 0
+; CHECK-ASM32-NEXT:     .byte 0x01                            # NumberOfFPParms = 0, +HasParmsOnStack
+; CHECK-ASM32-NEXT:     .vbyte  4, L..varalloca0-.varalloca     # Function size
+; CHECK-ASM32-NEXT:     .vbyte  2, 0x0009                       # Function name len = 9
+; CHECK-ASM32-NEXT:     .byte "varalloca"                     # Function Name
+; CHECK-ASM32-NEXT:     .byte 0x1f                            # AllocaUsed
+; CHECK-ASM32-NEXT:                                            # -- End function
+;
+; CHECK-ASM64-LABEL: varalloca:
+; CHECK-ASM64:       # %bb.0: # %entry
+; CHECK-ASM64-NEXT:    std 31, -8(1)
+; CHECK-ASM64-NEXT:    stdu 1, -64(1)
+; CHECK-ASM64-NEXT:    ld 3, L..C0(2) # @var
+; CHECK-ASM64-NEXT:    mr 31, 1
+; CHECK-ASM64-NEXT:    addi 4, 31, 64
+; CHECK-ASM64-NEXT:    lwz 3, 0(3)
+; CHECK-ASM64-NEXT:    addi 3, 3, 15
+; CHECK-ASM64-NEXT:    rldicl 3, 3, 60, 4
+; CHECK-ASM64-NEXT:    rldicl 3, 3, 4, 31
+; CHECK-ASM64-NEXT:    neg 3, 3
+; CHECK-ASM64-NEXT:    stdux 4, 1, 3
+; CHECK-ASM64-NEXT:    addi 3, 1, 48
+; CHECK-ASM64-NEXT:    lwz 3, 0(3)
+; CHECK-ASM64-NEXT:    ld 1, 0(1)
+; CHECK-ASM64-NEXT:    ld 31, -8(1)
+; CHECK-ASM64-NEXT:    blr
+; CHECK-ASM64-NEXT:    L..varalloca0:
+; CHECK-ASM64-NEXT:     .vbyte  4, 0x00000000                   # Traceback table begin
+; CHECK-ASM64-NEXT:     .byte 0x00                            # Version = 0
+; CHECK-ASM64-NEXT:     .byte 0x09                            # Language = CPlusPlus
+; CHECK-ASM64-NEXT:     .byte 0x20                            # -IsGlobaLinkage, -IsOutOfLineEpilogOrPrologue
+; CHECK-ASM64-NEXT:                                            # +HasTraceBackTableOffset, -IsInternalProcedure
+; CHECK-ASM64-NEXT:                                            # -HasControlledStorage, -IsTOCless
+; CHECK-ASM64-NEXT:                                            # -IsFloatingPointPresent
+; CHECK-ASM64-NEXT:                                            # -IsFloatingPointOperationLogOrAbortEnabled
+; CHECK-ASM64-NEXT:     .byte 0x60                            # -IsInterruptHandler, +IsFunctionNamePresent, +IsAllocaUsed
+; CHECK-ASM64-NEXT:                                            # OnConditionDirective = 0, -IsCRSaved, -IsLRSaved
+; CHECK-ASM64-NEXT:     .byte 0x80                            # +IsBackChainStored, -IsFixup, NumOfFPRsSaved = 0
+; CHECK-ASM64-NEXT:     .byte 0x01                            # -HasExtensionTable, -HasVectorInfo, NumOfGPRsSaved = 1
+; CHECK-ASM64-NEXT:     .byte 0x00                            # NumberOfFixedParms = 0
+; CHECK-ASM64-NEXT:     .byte 0x01                            # NumberOfFPParms = 0, +HasParmsOnStack
+; CHECK-ASM64-NEXT:     .vbyte  4, L..varalloca0-.varalloca     # Function size
+; CHECK-ASM64-NEXT:     .vbyte  2, 0x0009                       # Function name len = 9
+; CHECK-ASM64-NEXT:     .byte "varalloca"                     # Function Name
+; CHECK-ASM64-NEXT:     .byte 0x1f                            # AllocaUsed
+; CHECK-ASM64-NEXT:                                            # -- End function
+entry:
+  %0 = load i32, i32* @var
+  %1 = alloca i8, i32 %0
+  %2 = bitcast i8* %1 to i32*
+  %3 = load i32, i32* %2
+  ret i32 %3
+}
+

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

 ; COMMON:       .vbyte  4, 0x00000000                   # Traceback table begin
 ; COMMON-NEXT:  .byte   0x00                            # Version = 0
 ; COMMON-NEXT:  .byte   0x09                            # Language = CPlusPlus
 ; COMMON-NEXT:  .byte   0x22                            # -IsGlobaLinkage, -IsOutOfLineEpilogOrPrologue
 ; COMMON-NEXT:                                        # +HasTraceBackTableOffset, -IsInternalProcedure
 ; COMMON-NEXT:                                        # -HasControlledStorage, -IsTOCless
 ; COMMON-NEXT:                                        # +IsFloatingPointPresent
 ; COMMON-NEXT:                                        # -IsFloatingPointOperationLogOrAbortEnabled
-; COMMON-NEXT:  .byte   0x60                            # -IsInterruptHandler, +IsFunctionNamePresent, +IsAllocaUsed
+; COMMON-NEXT:  .byte   0x40                            # -IsInterruptHandler, +IsFunctionNamePresent, -IsAllocaUsed
 ; COMMON-NEXT:                                        # OnConditionDirective = 0, -IsCRSaved, -IsLRSaved
 ; COMMON-NEXT:  .byte   0x85                            # +IsBackChainStored, -IsFixup, NumOfFPRsSaved = 5
 ; COMMON-NEXT:  .byte   0x04                            # -HasExtensionTable, -HasVectorInfo, NumOfGPRsSaved = 4
 ; COMMON-NEXT:  .byte   0x00                            # NumberOfFixedParms = 0
 ; COMMON-NEXT:  .byte   0x01                            # NumberOfFPParms = 0, +HasParmsOnStack
 ; CHECK-ASM-NEXT:   .vbyte  4, L..bar0-.bar                 # Function size
 ; CHECK-FUNC-NEXT:  .vbyte  4, L..bar0-.bar[PR]             # Function size
 ; COMMON-NEXT:  .vbyte  2, 0x0003                       # Function name len = 3
 ; COMMON-NEXT:  .byte   "bar"                           # Function Name
-; COMMON-NEXT:  .byte   0x1f                            # AllocaUsed
 ; COMMON-NEXT:                                        # -- End function
 
 ; COMMON:     L..foov0:
 ; COMMON-NEXT:  .vbyte  4, 0x00000000                   # Traceback table begin
 ; COMMON-NEXT:  .byte   0x00                            # Version = 0
 ; COMMON-NEXT:  .byte   0x09                            # Language = CPlusPlus
 ; COMMON-NEXT:  .byte   0x20                            # -IsGlobaLinkage, -IsOutOfLineEpilogOrPrologue
 ; COMMON-NEXT:                                         # +HasTraceBackTableOffset, -IsInternalProcedure