[ELF] Actually sort IRELATIVE by offset

The unstable partition in partitionRels might reverse IRELATIVE
relocations, so stable_partition in computeRels would lead to IRELATIVE
relocations ordered by decreasing offset. Use stable_partition in
partitionRels to get IRELATIVE relocations ordered by increasing offset.

Author: MaskRay

lld/ELF/SyntheticSections.cpp

@@ -1633,7 +1633,8 @@ void RelocationBaseSection::partitionRels() {
     return;
   const RelType relativeRel = target->relativeRel;
   numRelativeRelocs =
-      llvm::partition(relocs, [=](auto &r) { return r.type == relativeRel; }) -
+      std::stable_partition(relocs.begin(), relocs.end(),
+                            [=](auto &r) { return r.type == relativeRel; }) -
       relocs.begin();
 }
 

lld/test/ELF/gnu-ifunc-nonpreemptible.s

@@ -23,12 +23,13 @@
 # RUN: ld.lld -shared a.o b.so -o a2
 # RUN: llvm-readelf -rs a2 | FileCheck %s --check-prefix=PIC
 
-# PIC:                                 R_X86_64_GLOB_DAT      0000000000000000 ext + 0
-# PIC-NEXT: {{0*}}[[#%x,O:]]  [[#%x,]] R_X86_64_64            0000000000000000 __rela_iplt_start + 0
-# PIC-NEXT: {{0*}}[[#O+8]]    [[#%x,]] R_X86_64_64            0000000000000000 __rela_iplt_end + 0
-# PIE-NEXT: {{0*}}[[#O+16]]   [[#%x,]] R_X86_64_IRELATIVE
-# PIE-NEXT: {{0*}}[[#O+24]]   [[#%x,]] R_X86_64_IRELATIVE
-# PIE-NEXT: {{0*}}[[#O+32]]   [[#%x,]] R_X86_64_IRELATIVE
+# PIC:      {{0*}}[[#%x,O:]] [[#%x,]] R_X86_64_RELATIVE
+# PIC-NEXT:                           R_X86_64_GLOB_DAT      0000000000000000 ext + 0
+# PIC-NEXT: {{0*}}[[#O-16]]  [[#%x,]] R_X86_64_64            0000000000000000 __rela_iplt_start + 0
+# PIC-NEXT: {{0*}}[[#O-8]]   [[#%x,]] R_X86_64_64            0000000000000000 __rela_iplt_end + 0
+# PIE-NEXT: {{0*}}[[#O+8]]   [[#%x,]] R_X86_64_IRELATIVE
+# PIE-NEXT: {{0*}}[[#O+16]]  [[#%x,]] R_X86_64_IRELATIVE
+# PIE-NEXT: {{0*}}[[#O+24]]  [[#%x,]] R_X86_64_IRELATIVE
 
 # PIC:        0 NOTYPE  WEAK   DEFAULT    UND __rela_iplt_start
 # PIC-NEXT:   0 NOTYPE  WEAK   DEFAULT    UND __rela_iplt_end
@@ -83,6 +84,7 @@ _start:
 .data
   .quad __rela_iplt_start
   .quad __rela_iplt_end
+  .quad .data
 
 #--- b.s
 .globl ext