[PATCH] D23732: [ELF] ICF should respect section alignment

[Petr Hosek via llvm-commits]

phosek created this revision.
phosek added reviewers: ruiu, rafael.
phosek added subscribers: llvm-commits, phosek.
phosek added a project: lld.

When performing ICF, we have to respect the alignment requirement of each section within each group.

https://reviews.llvm.org/D23732

Files:
  ELF/ICF.cpp
  test/ELF/icf7.s

Index: test/ELF/icf7.s
===================================================================
--- test/ELF/icf7.s
+++ test/ELF/icf7.s
@@ -4,8 +4,8 @@
 # RUN: ld.lld %t -o %t2 --icf=all --verbose | FileCheck %s
 # RUN: llvm-objdump -t %t2 | FileCheck -check-prefix=ALIGN %s
 
-# CHECK: selected .text.f1
-# CHECK:   removed .text.f2
+# CHECK: selected .text.f2
+# CHECK:   removed .text.f1
 
 # ALIGN: 0000000000011000 .text 00000000 _start
 # ALIGN: 0000000000011100 .text 00000000 f1
Index: ELF/ICF.cpp
===================================================================
--- ELF/ICF.cpp
+++ ELF/ICF.cpp
@@ -302,7 +302,12 @@
   // the same group are consecutive in the vector.
   std::stable_sort(V.begin(), V.end(),
                    [](InputSection<ELFT> *A, InputSection<ELFT> *B) {
-                     return A->GroupId < B->GroupId;
+                     if (A->GroupId != B->GroupId)
+                       return A->GroupId < B->GroupId;
+                     else
+                       // Within a group, put the highest alignment
+                       // requirement first, so that's the one we'll keep.
+                       return B->Alignment < A->Alignment;
                    });
 
   // Compare static contents and assign unique IDs for each static content.


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