[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

diff --git a/llvm/lib/MC/MCObjectFileInfo.cpp b/llvm/lib/MC/MCObjectFileInfo.cpp
index c910bd8..d3b9fa4 100644 (file)
--- 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 *

diff --git a/llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll b/llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll
index 456c99d..faf770f 100644 (file)
--- a/llvm/test/Transforms/SampleProfile/pseudo-probe-emit.ll
+++ b/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 -g %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 -g %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 @@ entry:
   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 +102,43 @@ entry:
 ; 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 PROGBITS
+; 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-SEC:       COMDAT group section [    7] `.group' [foo3] contains 2 sections:
+; CHECK-SEC-NEXT:     [Index]    Name
+; CHECK-SEC-NEXT:     [    8]   .text.foo3
+; CHECK-SEC-NEXT:     [   21]   .pseudo_probe
+; CHECK-SEC-EMPTY:
+; CHECK-SEC-NEXT:  COMDAT group section [   10] `.group' [.pseudo_probe_desc_foo] contains 1 sections:
+; CHECK-SEC-NEXT:     [Index]    Name
+; CHECK-SEC-NEXT:     [   11]   .pseudo_probe_desc
+; CHECK-SEC-EMPTY:
+; CHECK-SEC-NEXT:  COMDAT group section [   12] `.group' [.pseudo_probe_desc_foo2] contains 1 sections:
+; CHECK-SEC-NEXT:     [Index]    Name
+; CHECK-SEC-NEXT:     [   13]   .pseudo_probe_desc
+; CHECK-SEC-EMPTY:
+; CHECK-SEC-NEXT:  COMDAT group section [   14] `.group' [.pseudo_probe_desc_foo3] contains 1 sections:
+; CHECK-SEC-NEXT:     [Index]    Name
+; CHECK-SEC-NEXT:     [   15]   .pseudo_probe_desc
+
+
+; 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 PROGBITS
+; 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}