[PATCH] D153189: [MC] Make .pseudo_probe GC-able

[Fangrui Song via Phabricator via llvm-commits]

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- 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 (disambiguiated by `.section ....,unique,id` in assembly)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D153189

Files:
  llvm/lib/MC/MCObjectFileInfo.cpp
  llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll


Index: llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll
===================================================================
--- llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll
+++ llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll
@@ -5,9 +5,12 @@
 ; RUN: llc %t -function-sections -filetype=asm -o %t1
 ; RUN: FileCheck %s < %t1 --check-prefix=CHECK-ASM
 ; RUN: llc %t -function-sections -filetype=obj -o %t2
-; RUN: llvm-objdump --section-headers  %t2 | FileCheck %s --check-prefix=CHECK-OBJ
+; RUN: llvm-readelf -S  %t2 | FileCheck %s --check-prefix=CHECK-SEC
 ; RUN: llvm-mc %t1 -filetype=obj -o %t3
-; RUN: llvm-objdump --section-headers  %t3 | FileCheck %s --check-prefix=CHECK-OBJ
+; RUN: llvm-readelf -S  %t3 | FileCheck %s --check-prefix=CHECK-SEC
+
+; RUN: llc %t -function-sections -unique-section-names=0 -filetype=obj -o %t4
+; RUN: llvm-readelf -S  %t4 | FileCheck %s --check-prefix=CHECK-SEC2
 
 ;; Check the generation of pseudoprobe intrinsic call.
 
@@ -64,6 +67,13 @@
   ret void
 }
 
+$foo3 = comdat any
+
+define void @foo3(i32 %x) comdat {
+entry:
+  ret void
+}
+
 ; CHECK-IL: Function Attrs: nocallback nofree nosync nounwind willreturn memory(inaccessiblemem: readwrite)
 ; CHECK-IL-NEXT: declare void @llvm.pseudoprobe(i64, i64, i32, i64)
 
@@ -92,9 +102,25 @@
 ; CHECK-ASM-NEXT: .byte 4
 ; CHECK-ASM-NEXT: .ascii	"foo2"
 
-; CHECK-OBJ-COUNT-2: .pseudo_probe_desc
-; CHECK-OBJ: .pseudo_probe
-; CHECK-OBJ-NOT: .rela.pseudo_probe
+; CHECK-SEC:          [Nr] Name              Type     {{.*}} ES Flg Lk Inf Al
+; CHECK-SEC:          [ 3] .text.foo         PROGBITS {{.*}} 00  AX  0   0 16
+; CHECK-SEC:          [ 5] .text.foo2        PROGBITS {{.*}} 00  AX  0   0 16
+; CHECK-SEC:          [ 8] .text.foo3        PROGBITS {{.*}} 00  AXG 0   0 16
+; CHECK-SEC-COUNT-3:       .pseudo_probe_desc
+; CHECK-SEC:                .pseudo_probe    PROGBITS {{.*}} 00   L  3   0  1
+; CHECK-SEC-NEXT:           .pseudo_probe    PROGBITS {{.*}} 00   L  5   0  1
+; CHECK-SEC-NEXT:           .pseudo_probe    PROGBITS {{.*}} 00   LG 8   0  1
+; CHECK-SEC-NOT:     .rela.pseudo_probe
+
+; CHECK-SEC2:         [Nr] Name              Type     {{.*}} ES Flg Lk Inf Al
+; CHECK-SEC2:         [ 3] .text             PROGBITS {{.*}} 00  AX  0   0 16
+; CHECK-SEC2:         [ 5] .text             PROGBITS {{.*}} 00  AX  0   0 16
+; CHECK-SEC2:         [ 8] .text             PROGBITS {{.*}} 00  AXG 0   0 16
+; CHECK-SEC2-COUNT-3:      .pseudo_probe_desc
+; CHECK-SEC2:               .pseudo_probe    PROGBITS {{.*}} 00   L  3   0  1
+; CHECK-SEC2-NEXT:          .pseudo_probe    PROGBITS {{.*}} 00   L  5   0  1
+; CHECK-SEC2-NEXT:          .pseudo_probe    PROGBITS {{.*}} 00   LG 8   0  1
+; CHECK-SEC2-NOT:     .rela.pseudo_probe
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!9, !10}
Index: llvm/lib/MC/MCObjectFileInfo.cpp
===================================================================
--- llvm/lib/MC/MCObjectFileInfo.cpp
+++ llvm/lib/MC/MCObjectFileInfo.cpp
@@ -1165,18 +1165,20 @@
 
 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 *


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