From f599bfcd273a502aebb392b901e39240a0074710 Mon Sep 17 00:00:00 2001
From: Fangrui Song <i@maskray.me>
Date: Tue, 24 Mar 2026 21:59:03 -0700
Subject: [PATCH] [ELF] Guard relocation section handling behind copyRelocs in
 addOrphanSections. NFC (#188409)

In addOrphanSections, getRelocatedSection() only returns non-null for -r
or --emit-relocs links. Guard code blocks with `copyRelocs` to skip
unnecessary dyn_cast + getRelocatedSection calls per section in the
common case. Hoist copyRelocs and relocatable to local variables so the
compiler does not reload them through ctx on every loop iteration.

"Assign sections" decreases by 1ms.
---
 lld/ELF/LinkerScript.cpp | 50 ++++++++++++++++++++++------------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 76f04a27b999..23b59349ab0b 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -50,8 +50,11 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
   // This is for --emit-relocs and -r. If .text.foo is emitted as .text.bar, we
   // want to emit .rela.text.foo as .rela.text.bar for consistency (this is not
   // technically required, but not doing it is odd). This code guarantees that.
-  if (auto *isec = dyn_cast<InputSection>(s)) {
-    if (InputSectionBase *rel = isec->getRelocatedSection()) {
+  if (LLVM_UNLIKELY(ctx.arg.copyRelocs)) {
+    InputSectionBase *rel = nullptr;
+    if (auto *isec = dyn_cast<InputSection>(s))
+      rel = isec->getRelocatedSection();
+    if (rel) {
       OutputSection *out = rel->getOutputSection();
       if (!out) {
         assert(ctx.arg.relocatable && (rel->flags & SHF_LINK_ORDER));
@@ -64,11 +67,10 @@ StringRef LinkerScript::getOutputSectionName(const InputSectionBase *s) const {
         return ss.save(".rela" + out->name);
       return ss.save(".rel" + out->name);
     }
+    if (ctx.arg.relocatable)
+      return s->name;
   }
 
-  if (ctx.arg.relocatable)
-    return s->name;
-
   // A BssSection created for a common symbol is identified as "COMMON" in
   // linker scripts. It should go to .bss section.
   if (s->name == "COMMON")
@@ -1021,32 +1023,36 @@ void LinkerScript::addOrphanSections() {
     }
   };
 
+  const bool copyRelocs = ctx.arg.copyRelocs;
+  const bool relocatable = ctx.arg.relocatable;
   size_t n = 0;
   for (InputSectionBase *isec : ctx.inputSections) {
     // Process InputSection and MergeInputSection.
     if (LLVM_LIKELY(isa<InputSection>(isec)))
       ctx.inputSections[n++] = isec;
 
-    // In -r links, SHF_LINK_ORDER sections are added while adding their parent
-    // sections because we need to know the parent's output section before we
-    // can select an output section for the SHF_LINK_ORDER section.
-    if (ctx.arg.relocatable && (isec->flags & SHF_LINK_ORDER))
-      continue;
+    if (LLVM_UNLIKELY(copyRelocs)) {
+      // In -r links, SHF_LINK_ORDER sections are added while adding their
+      // parent sections because we need to know the parent's output section
+      // before we can select an output section for the SHF_LINK_ORDER section.
+      if (relocatable && (isec->flags & SHF_LINK_ORDER))
+        continue;
 
-    if (auto *sec = dyn_cast<InputSection>(isec)) {
-      if (InputSectionBase *relocated = sec->getRelocatedSection()) {
-        // For --emit-relocs and -r, ensure the output section for .text.foo
-        // is created before the output section for .rela.text.foo.
-        add(relocated);
-        // EhInputSection sections are not added to ctx.inputSections. If we see
-        // .rela.eh_frame, ensure the output section for the synthetic
-        // EhFrameSection is created first.
-        if (auto *p = dyn_cast_or_null<InputSectionBase>(relocated->parent))
-          add(p);
-      }
+      if (auto *sec = dyn_cast<InputSection>(isec))
+        if (InputSectionBase *relocated = sec->getRelocatedSection()) {
+          // For --emit-relocs and -r, ensure the output section for .text.foo
+          // is created before the output section for .rela.text.foo.
+          add(relocated);
+          // EhInputSection sections are not added to ctx.inputSections. If we
+          // see .rela.eh_frame, ensure the output section for the synthetic
+          // EhFrameSection is created first.
+          if (auto *p = dyn_cast_or_null<InputSectionBase>(relocated->parent))
+            add(p);
+        }
     }
+
     add(isec);
-    if (ctx.arg.relocatable)
+    if (LLVM_UNLIKELY(relocatable))
       for (InputSectionBase *depSec : isec->dependentSections)
         if (depSec->flags & SHF_LINK_ORDER)
           add(depSec);