From 0cc063a8ffc896aa82ebe4b11003f0bbd78d6d5b Mon Sep 17 00:00:00 2001
From: Snehasish Kumar <snehasishk@google.com>
Date: Fri, 24 Apr 2020 14:35:19 -0700
Subject: Use .text.unlikely and .text.eh prefixes for MachineBasicBlock
 sections.

Summary:
Instead of adding a ".unlikely" or ".eh" suffix for machine basic blocks,
this change updates the behaviour to use an appropriate prefix
instead. This allows lld to group basic block sections together
when -z,keep-text-section-prefix is specified and matches the behaviour
observed in gcc.

Reviewers: tmsriram, mtrofin, efriedma

Reviewed By: tmsriram, efriedma

Subscribers: eli.friedman, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78742
---
 llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp | 32 +++++++++++------------
 1 file changed, 16 insertions(+), 16 deletions(-)

(limited to 'llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp')

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 8ed3e8673a84..a2dfa0a5734f 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -859,28 +859,28 @@ MCSection *TargetLoweringObjectFileELF::getSectionForMachineBasicBlock(
     const Function &F, const MachineBasicBlock &MBB,
     const TargetMachine &TM) const {
   assert(MBB.isBeginSection() && "Basic block does not start a section!");
-  SmallString<128> Name;
-  Name =
-      (static_cast<MCSectionELF *>(MBB.getParent()->getSection()))->getName();
   unsigned UniqueID = MCContext::GenericSectionID;
 
-  switch (MBB.getSectionID().Type) {
-    // Append suffixes to represent special cold and exception sections.
-  case MBBSectionID::SectionType::Exception:
-    Name += ".eh";
-    break;
-  case MBBSectionID::SectionType::Cold:
-    Name += ".unlikely";
-    break;
-  // For regular sections, either use a unique name, or a unique ID for the
-  // section.
-  default:
+  // For cold sections use the .text.unlikely prefix along with the parent
+  // function name. All cold blocks for the same function go to the same
+  // section. Similarly all exception blocks are grouped by symbol name
+  // under the .text.eh prefix. For regular sections, we either use a unique
+  // name, or a unique ID for the section.
+  SmallString<128> Name;
+  if (MBB.getSectionID() == MBBSectionID::ColdSectionID) {
+    Name += ".text.unlikely.";
+    Name += MBB.getParent()->getName();
+  } else if (MBB.getSectionID() == MBBSectionID::ExceptionSectionID) {
+    Name += ".text.eh.";
+    Name += MBB.getParent()->getName();
+  } else {
+    Name += MBB.getParent()->getSection()->getName();
     if (TM.getUniqueBBSectionNames()) {
       Name += ".";
       Name += MBB.getSymbol()->getName();
-    } else
+    } else {
       UniqueID = NextUniqueID++;
-    break;
+    }
   }
 
   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_EXECINSTR;
-- 
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