[Pseudo Probe] Make .pseudo_probe GC-able

* Add the SHF_LINK_ORDER flag so that the .pseudo_probe section is discarded when the associated text section is discarded.
* Add unique ID so that with `clang -ffunction-sections -fno-unique-section-names`, there is one separate .pseudo_probe for each text section (disambiguated by `.section ....,unique,id` in assembly)

The changes allow .pseudo_probe GC even if we don't place instrumented functions
in an IR comdat (see `getOrCreateFunctionComdat` in SampleProfileProbe.cpp).

Reviewed By: hoy

Differential Revision: https://reviews.llvm.org/D153189

1 files changed, 13 insertions, 11 deletions

diff --git a/llvm/lib/MC/MCObjectFileInfo.cpp b/llvm/lib/MC/MCObjectFileInfo.cpp
index c910bd8..d3b9fa45 100644
--- a/llvm/lib/MC/MCObjectFileInfo.cpp
+++ b/llvm/lib/MC/MCObjectFileInfo.cpp
@@ -1165,18 +1165,20 @@ MCObjectFileInfo::getKCFITrapSection(const MCSection &TextSec) const {
 
 MCSection *
 MCObjectFileInfo::getPseudoProbeSection(const MCSection &TextSec) const {
-  if (Ctx->getObjectFileType() == MCContext::IsELF) {
-    const auto &ElfSec = static_cast<const MCSectionELF &>(TextSec);
-    // Create a separate section for probes that comes with a comdat function.
-    if (const MCSymbol *Group = ElfSec.getGroup()) {
-      auto *S = static_cast<MCSectionELF *>(PseudoProbeSection);
-      auto Flags = S->getFlags() | ELF::SHF_GROUP;
-      return Ctx->getELFSection(S->getName(), S->getType(), Flags,
-                                S->getEntrySize(), Group->getName(),
-                                /*IsComdat=*/true);
-    }
+  if (Ctx->getObjectFileType() != MCContext::IsELF)
+    return PseudoProbeSection;
+
+  const auto &ElfSec = static_cast<const MCSectionELF &>(TextSec);
+  unsigned Flags = ELF::SHF_LINK_ORDER;
+  StringRef GroupName;
+  if (const MCSymbol *Group = ElfSec.getGroup()) {
+    GroupName = Group->getName();
+    Flags |= ELF::SHF_GROUP;
   }
-  return PseudoProbeSection;
+
+  return Ctx->getELFSection(PseudoProbeSection->getName(), ELF::SHT_PROGBITS,
+                            Flags, 0, GroupName, true, ElfSec.getUniqueID(),
+                            cast<MCSymbolELF>(TextSec.getBeginSymbol()));
 }
 
 MCSection *