[Coverage] Mark coverage sections as metadata sections on COFF.

[ZequanWu]

Mark .lcovmap$M, .lcovfun$M, .lcovd and .lcovn as metadata sections on COFF so they are not loaded into memory.

[llvmbot]

@llvm/pr-subscribers-backend-x86

Author: Zequan Wu (ZequanWu)

Changes

Mark .lcovmap$M, .lcovfun$M, .lcovd and .lcovn as metadata sections on COFF so they are not loaded into memory.

---

Full diff: https://github.com/llvm/llvm-project/pull/76834.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (+10-1)
• (added) llvm/test/CodeGen/X86/cov-sections.ll (+15)

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 6e69dc66429d31..a69b71451736fa 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -1669,9 +1669,18 @@ static int getSelectionForCOFF(const GlobalValue *GV) {
 
 MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
+  StringRef Name = GO->getSection();
+  if (Name == getInstrProfSectionName(IPSK_covmap, Triple::COFF,
+                                      /*AddSegmentInfo=*/false) ||
+      Name == getInstrProfSectionName(IPSK_covfun, Triple::COFF,
+                                      /*AddSegmentInfo=*/false) ||
+      Name == getInstrProfSectionName(IPSK_covdata, Triple::COFF,
+                                      /*AddSegmentInfo=*/false) ||
+      Name == getInstrProfSectionName(IPSK_covname, Triple::COFF,
+                                      /*AddSegmentInfo=*/false))
+    Kind = SectionKind::getMetadata();
   int Selection = 0;
   unsigned Characteristics = getCOFFSectionFlags(Kind, TM);
-  StringRef Name = GO->getSection();
   StringRef COMDATSymName = "";
   if (GO->hasComdat()) {
     Selection = getSelectionForCOFF(GO);
diff --git a/llvm/test/CodeGen/X86/cov-sections.ll b/llvm/test/CodeGen/X86/cov-sections.ll
new file mode 100644
index 00000000000000..6c4f3f079f38e3
--- /dev/null
+++ b/llvm/test/CodeGen/X86/cov-sections.ll
@@ -0,0 +1,15 @@
+; RUN: llc < %s -mtriple=x86_64-pc-windows-msvc -filetype=obj -o - | llvm-readobj -S - | FileCheck %s
+
+@covmap = private global i32 0, section ".lcovmap$M"
+@covfun = private global i32 0, section ".lcovfun$M"
+@covname = private global i32 0, section ".lcovd"
+@covdata= private global i32 0, section ".lcovn"
+
+; CHECK: Name: .lcovmap$M
+; CHECK: IMAGE_SCN_MEM_DISCARDABLE (0x2000000)
+; CHECK: Name: .lcovfun$M
+; CHECK: IMAGE_SCN_MEM_DISCARDABLE (0x2000000)
+; CHECK: Name: .lcovd
+; CHECK: IMAGE_SCN_MEM_DISCARDABLE (0x2000000)
+; CHECK: Name: .lcovn
+; CHECK: IMAGE_SCN_MEM_DISCARDABLE (0x2000000)

[rnk]

Arthur, is there a better way to set section flags in LLVM IR, or at least a better place to store special case known section names to assign their characteristics?

cc @MaskRay , perhaps you have ideas

[aeubanks]

I don't think it makes sense to put this in the IR, choosing when emitting an object file seems like the right place to make this decision

this looks in line with existing SectionKind overrides per object file format (e.g. getELFKindForNamedSection, TargetLoweringObjectFileWasm::getExplicitSectionGlobal). TargetLoweringObjectFile::getKindForGlobal() is where the common logic is, and there's an argument to be made to consolidate all of the per object file format overrides into that method, but I also think this is fine