[PseudoProbe] Only emit discriminstor in FS-AFDO mode.

[hoy]

Summary

Despite previous effort D148569: [PseudoProbe] Clean up dwarf discriminator and avoid duplicating factor. to avoid screwing up existing disrminator field, I'm still seeing some call probes getting a non-zero discriminator eventually in non-FS mode. It could be related to callsite merge. While they are investigated I'm disabling discriminator emission for non-FS mode. This avoids breaking the compatiblity with older tools like llvm-profgen and bolt.

[hoy]

Switching to checking block probe for discriminator emission.

[wenlei]

thanks for the fix, lgtm.

llvm/lib/CodeGen/AsmPrinter/PseudoProbePrinter.cpp

49

should we put in an assert to make sure we catch lurking non-zero discriminators? i.e. when FS is off, probe should always have zero discriminator?

[hoy]

llvm/lib/CodeGen/AsmPrinter/PseudoProbePrinter.cpp

49

Good point. Actually there is already an assert on IR level https://github.com/llvm/llvm-project/blob/b7d9322b4963e620dfd12246816e6f7b2da5fd88/llvm/lib/IR/PseudoProbe.cpp#L67, let me also add an assert here for MIR.

[hoy]

Adding assert.

llvm/lib/CodeGen/AsmPrinter/PseudoProbePrinter.cpp

while (InlinedAt) {
     uint64_t CallerProbeId = PseudoProbeDwarfDiscriminator::extractProbeIndex(
         InlinedAt->getDiscriminator());
     ReversedInlineStack.emplace_back(CallerGuid, CallerProbeId);
     InlinedAt = InlinedAt->getInlinedAt();
   }
   uint64_t Discriminator = 0;
   // For now only block probes have FS discriminators. See
   // MIRFSDiscriminator.cpp for more details.
-  if (DebugLoc &&
-      !DILocation::isPseudoProbeDiscriminator(DebugLoc->getDiscriminator()))
+  if (EnableFSDiscriminator && DebugLoc &&
+      (Type == (uint64_t)PseudoProbeType::Block))
     Discriminator = DebugLoc->getDiscriminator();
+  assert((EnableFSDiscriminator || Discriminator == 0) &&
+         "Discriminator should not be set in non-FSAFDO mode");
   SmallVector<InlineSite, 8> InlineStack(llvm::reverse(ReversedInlineStack));
   Asm->OutStreamer->emitPseudoProbe(Guid, Index, Type, Attr, Discriminator,
                                     InlineStack, Asm->CurrentFnSym);
 }