Remove unnecessary and incorrect sorting of input sections

This commit removes the unnecessary and incorrect sorting of input
sections before the merge input sections phase when the LTO is enabled.

Resolves #1204

Signed-off-by: Parth Arora <partaror@qti.qualcomm.com>

Author: parth-07

include/eld/Object/ObjectLinker.h

@@ -269,8 +269,6 @@ class ObjectLinker {
   bool mergeInputSections(ObjectBuilder &Builder,
                           std::vector<Section *> &Sections);
 
-  bool mayBeSortSections(std::vector<Section *> &Sections);
-
   bool createOutputSection(ObjectBuilder &Builder, OutputSectionEntry *Output,
                            bool PostLayout = false);
 

lib/Object/ObjectLinker.cpp

@@ -784,44 +784,6 @@ void ObjectLinker::markDiscardFileFormatSections() {
   }
 }
 
-bool ObjectLinker::mayBeSortSections(std::vector<Section *> &Sections) {
-  // If no linker scripts, we dont store the original input. Lets not sort.
-  if (!ThisModule->getScript().linkerScriptHasSectionsCommand())
-    return true;
-  if (ThisConfig.options().disableLTOLinkOrder())
-    return true;
-  // If we are doing partial link, lets not sort it.
-  bool IsPartialLink = (LinkerConfig::Object == ThisConfig.codeGenType());
-  if (IsPartialLink || LtoObjects.empty())
-    return true;
-  std::stable_sort(Sections.begin(), Sections.end(),
-                   [](Section *ASection, Section *BSection) {
-                     ELFSection *A = llvm::dyn_cast<ELFSection>(ASection);
-                     ELFSection *B = llvm::dyn_cast<ELFSection>(BSection);
-                     if (A == nullptr or B == nullptr)
-                       return false;
-                     // FIXME: Redundant checks. All files have original input.
-                     if (!A->originalInput())
-                       return false;
-                     if (!B->originalInput())
-                       return false;
-                     if ((A->name().starts_with(".ctors")) ||
-                         (B->name().starts_with(".ctors")))
-                       return false;
-                     if ((A->name().starts_with(".dtors")) ||
-                         (B->name().starts_with(".dtors")))
-                       return false;
-                     int64_t AOrdinal =
-                         A->originalInput()->getInput()->getInputOrdinal();
-                     int64_t BOrdinal =
-                         B->originalInput()->getInput()->getInputOrdinal();
-                     if (AOrdinal == BOrdinal)
-                       return false;
-                     return (AOrdinal < BOrdinal);
-                   });
-  return true;
-}
-
 bool ObjectLinker::mergeInputSections(ObjectBuilder &Builder,
                                       std::vector<Section *> &Sections) {
   bool IsPartialLink = ThisConfig.isLinkPartial();
@@ -1112,12 +1074,6 @@ bool ObjectLinker::initializeMerge() {
       }
     }
   }
-  {
-    eld::RegisterTimer T("Sort sections if LTO enabled", "Merge Sections",
-                         ThisConfig.options().printTimingStats());
-    // Sort sections if we have LTO enabled.
-    mayBeSortSections(AllInputSections);
-  }
   return true;
 }
 

test/Common/LTO/LinkerScript/NonLTOSectionsOrderWithLTO/Inputs/2.c

@@ -0,0 +1 @@
+__attribute__((section(".ctors"))) int bar() { return 6; }

test/Common/LTO/LinkerScript/NonLTOSectionsOrderWithLTO/Inputs/3.c

@@ -0,0 +1 @@
+int baz() { return 5; }

test/Common/LTO/LinkerScript/NonLTOSectionsOrderWithLTO/Inputs/gen.py

@@ -0,0 +1,16 @@
+import sys
+
+N = 300
+output = sys.argv[1]
+
+with open(output, 'w') as f:
+    f.write("int bar();\n")
+    f.write("int baz();\n")
+    for i in range(N):
+        f.write(f"int foo_{i}() {{ return {i}; }}\n")
+    f.write("int main() {\n  return ")
+    for i in range(N):
+        f.write(f"foo_{i}()")
+        if i != N - 1:
+            f.write(" + ")
+    f.write(" + baz() + bar();\n}\n")

test/Common/LTO/LinkerScript/NonLTOSectionsOrderWithLTO/Inputs/script.t

@@ -0,0 +1,3 @@
+SECTIONS {
+  .text : { *(.text*) }
+}

test/Common/LTO/LinkerScript/NonLTOSectionsOrderWithLTO/NonLTOSectionsOrderWithLTO.test

@@ -0,0 +1,42 @@
+UNSUPPORTED: x86
+#---NonLTOSectionsOrderWithLTO.test------------- Executable,LTO,LS ----------------#
+#BEGIN_COMMENT
+# When a linker script rule matches input sections without explicit ordering,
+# the output should contain matched input sections in input order. With LTO,
+# ordering is relaxed for LTO-generated sections, but sections from non-LTO
+# object files must still maintain their original order. This test verifies
+# that non-LTO input section ordering is preserved when mixed with LTO objects.
+#END_COMMENT
+#START_TEST
+RUN: %python %p/Inputs/gen.py %t1.1.c
+RUN: %clang %clangopts -o %t1.1.o -c %t1.1.c -ffunction-sections
+RUN: %clang %clangopts -o %t1.2.o -c %p/Inputs/2.c -flto -ffunction-sections
+RUN: %clang %clangopts -o %t1.3.o -c %p/Inputs/3.c -flto -ffunction-sections
+RUN: %link -MapStyle txt %linkopts -o %t2.out %t1.2.o %t1.1.o %t1.3.o -T %p/Inputs/script.t -e main -Map %t2.map
+RUN: %filecheck %s < %t2.map
+#END_TEST
+
+CHECK: .text.foo_0
+CHECK: .text.foo_1
+CHECK: .text.foo_2
+CHECK: .text.foo_3
+CHECK: .text.foo_4
+CHECK: .text.foo_5
+CHECK: .text.foo_6
+CHECK: .text.foo_7
+CHECK: .text.foo_8
+CHECK: .text.foo_9
+CHECK: .text.foo_10
+CHECK: .text.foo_11
+CHECK: .text.foo_12
+CHECK: .text.foo_13
+CHECK: .text.foo_14
+CHECK: .text.foo_15
+CHECK: .text.foo_16
+CHECK: .text.foo_17
+CHECK: .text.foo_18
+CHECK: .text.foo_19
+CHECK: .text.foo_20
+CHECK: .text.foo_298
+CHECK: .text.foo_299
+CHECK: .text.main