[PATCH] D27145: Add "RPRED" mechanism for relocation predicates. (5% speedup for `ld.lld -O0`)

[Rui Ueyama via Phabricator via llvm-commits]

ruiu added a comment.

It is unfortunate that we cannot write like that. I wish we had the C99 desginated initializer in C++.



================
Comment at: ELF/Relocations.h:42-43
 enum RelExpr {
-  R_ABS,
-  R_GOT,
-  R_GOTONLY_PC,
-  R_GOTONLY_PC_FROM_END,
-  R_GOTREL,
-  R_GOTREL_FROM_END,
-  R_GOT_FROM_END,
-  R_GOT_OFF,
-  R_GOT_PAGE_PC,
-  R_GOT_PC,
-  R_HINT,
-  R_MIPS_GOT_LOCAL_PAGE,
-  R_MIPS_GOT_OFF,
-  R_MIPS_GOT_OFF32,
-  R_MIPS_GOTREL,
-  R_MIPS_TLSGD,
-  R_MIPS_TLSLD,
-  R_NEG_TLS,
-  R_PAGE_PC,
-  R_PC,
-  R_PLT,
-  R_PLT_PC,
-  R_PLT_PAGE_PC,
-  R_PPC_OPD,
-  R_PPC_PLT_OPD,
-  R_PPC_TOC,
-  R_RELAX_GOT_PC,
-  R_RELAX_GOT_PC_NOPIC,
-  R_RELAX_TLS_GD_TO_IE,
-  R_RELAX_TLS_GD_TO_IE_END,
-  R_RELAX_TLS_GD_TO_IE_ABS,
-  R_RELAX_TLS_GD_TO_IE_PAGE_PC,
-  R_RELAX_TLS_GD_TO_LE,
-  R_RELAX_TLS_GD_TO_LE_NEG,
-  R_RELAX_TLS_IE_TO_LE,
-  R_RELAX_TLS_LD_TO_LE,
-  R_SIZE,
-  R_THUNK_ABS,
-  R_THUNK_PC,
-  R_THUNK_PLT_PC,
-  R_TLS,
-  R_TLSDESC,
-  R_TLSDESC_PAGE,
-  R_TLSDESC_CALL,
-  R_TLSGD,
-  R_TLSGD_PC,
-  R_TLSLD,
-  R_TLSLD_PC,
+#define RELOCATION(Name, Index, PredicateBits) Name = (Index | PredicateBits),
+#include "Relocations.def"
 };
----------------
I think I prefer writing the definitions inline here in a macro-expanded form rather than in an included file. The file is not included more than once (except for static_assert), so the #include hack does not make much sense. I also want to make code less exciting by writing constants inline.

This code

  enum RelExprPredicateBit {
    RPRED_NEEDS_PLT       = 1 << 31,
    RPRED_ALWAYS_CONSTANT = 1 << 30,
    RPRED_REFERS_TO_GOT   = 1 << 29,
    RPRED_RELAX_MARKER    = 1 << 28,
    RPRED_RELATIVE        = 1 << 27,
  };

is boring but I believe it's easier to read. Likewise, I prefer a style like this because it is obvious what it is doing without looking at other places.

  enum RelExpr {
    R_ABS = 1,
    R_GOT = 2 | RPRED_REFERS_TO_GOT,
    R_GOTONLY_PC = 3,
    R_GOTONLY_PC_FROM_END = 4,
    R_GOTREL = 5 | RPRED_RELATIVE,
    R_GOTREL_FROM_END = 6 | RPRED_RELATIVE,
    R_GOT_FROM_END = 7 | RPRED_ALWAYS_CONSTANT | RPRED_REFERS_TO_GOT,
    ...
  };


https://reviews.llvm.org/D27145