[PATCH] D44965: [llvm][Instrumentation/MC] Add Call Graph Profile pass and object file emission.

[Michael Spencer via Phabricator via llvm-commits]

Bigcheese added a comment.

In writing the documentation I ran into an issue defining the precise semantics of `.cg_profile` when it includes a symbol which has not previously been referenced.  In an updated patch I'm treating it as if `.weak <symbol>` was written if <symbol> has not yet been used.  This leads to the following behavior:

  .section .test,"aw", at progbits
  a:    .word b
  
      .cg_profile a, b, 32
      .cg_profile freq, a, 11
      .cg_profile late, late2, 20
      .cg_profile .L.local, b, 42
  
      .globl late
  late:
  late2:
  late3:
  .L.local:

a: local
late3: local
b: global
freq: weak
late: global
late2: weak
.L.local: not in symbol table

Note that `a` and `late2` disagree about what binding they have based on if they came before or after `.cg_profile`.  Also `.L.local` generates a null symbol index because it doesn't get put in the symbol table.


https://reviews.llvm.org/D44965