[mips][ias] N32/N64 must not sort the relocation table.

[sdardis]

Summary

Doing so changes the evaluation order for relocation composition.

Patch By: Daniel Sanders

[atanasyan]

LGTM with a nit.

lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp

422 ↗

(On Diff #77195)

I would add a comment here to describe why we do not need to sort relocation if hasRelocationAddend() return true.

llvm/trunk/lib/Target/Mips/MCTargetDesc/MipsELFObjectWriter.cpp

 /// R_MIPS_GOT16 and similar only have AHL addends if they refer to local
 /// symbols.
 ///
 /// It should also be noted that this function is not affected by whether
 /// the symbol was kept or rewritten into a section-relative equivalent. We
 /// always match using the expressions from the source.
 void MipsELFObjectWriter::sortRelocs(const MCAssembler &Asm,
                                      std::vector<ELFRelocationEntry> &Relocs) {
+
+  // We do not need to sort the relocation table for RELA relocations which
+  // N32/N64 uses as the relocation addend contains the value we require,
+  // rather than it being split across a pair of relocations.
+  if (hasRelocationAddend())
+    return;
+
   if (Relocs.size() < 2)
     return;
 
   // Sort relocations by the address they are applied to.
   std::sort(Relocs.begin(), Relocs.end(),
             [](const ELFRelocationEntry &A, const ELFRelocationEntry &B) {
               return A.Offset < B.Offset;
             });

llvm/trunk/test/MC/Mips/reloc-directive.s

 #        incorrectly use the 3-reloc encoding (and ELF64). mips64-* triples
 #        are closest to being correct so we use them for now.
 #        This should be corrected once the triple bugfixes allow us to be ABI
 #        dependent rather than triple dependent.
 # OBJ-N32-LABEL: Name: .text
 # OBJ-N32:       0000: 00000000 00000000 00000000
 # OBJ-N32-LABEL: }
 # OBJ-N32-LABEL: Relocations [
-# OBJ-N32:       0x0 R_MIPS_NONE/R_MIPS_NONE/R_MIPS_NONE .text 0x4
+
 # OBJ-N32:       0x4 R_MIPS_NONE/R_MIPS_NONE/R_MIPS_NONE .text 0x0
+# OBJ-N32:       0x0 R_MIPS_NONE/R_MIPS_NONE/R_MIPS_NONE .text 0x4
 # OBJ-N32:       0x8 R_MIPS_32/R_MIPS_NONE/R_MIPS_NONE .text 0x8
 # OBJ-N32:       0xC R_MIPS_NONE/R_MIPS_NONE/R_MIPS_NONE -   0x0
 
+# FIXME:This is the correct output for reference.
+
+# OBJ-N32-FIXME:       0x4 R_MIPS_NONE .text 0x0
+# OBJ-N32-FIXME:       0x0 R_MIPS_NONE .text 0x4
+# OBJ-N32-FIXME:       0x8 R_MIPS_32   .text 0x8
+# OBJ-N32-FIXME:       0xC R_MIPS_NONE -     0x0
+
 # OBJ-N64-LABEL: Name: .text
 # OBJ-N64:       0000: 00000000 00000000 00000000
 # OBJ-N64-LABEL: }
 # OBJ-N64-LABEL: Relocations [
-# OBJ-N64:       0x0 R_MIPS_NONE/R_MIPS_NONE/R_MIPS_NONE .text 0x4
 # OBJ-N64:       0x4 R_MIPS_NONE/R_MIPS_NONE/R_MIPS_NONE .text 0x0
+# OBJ-N64:       0x0 R_MIPS_NONE/R_MIPS_NONE/R_MIPS_NONE .text 0x4
 # OBJ-N64:       0x8 R_MIPS_32/R_MIPS_NONE/R_MIPS_NONE .text 0x8
 # OBJ-N64:       0xC R_MIPS_NONE/R_MIPS_NONE/R_MIPS_NONE -   0x0