Generate correct relocation for external cost centre

We used to always generate direct access for cost centre labels.  We
fixed this by generating indirect data load for cost centre defined in
external module.

Test Plan:
The added test used to fail with error message
```
/bin/ld.gold: error: T15723B.o: requires dynamic R_X86_64_PC32 reloc
against 'T15723A_foo1_EXPR_cc' which may overflow at runtime; recompile
with -fPIC
```
and now passes.

Also check that `R_X86_64_PC32` is generated for CostCentre from the
same module and `R_X86_64_GOTPCREL` is generated for CostCentre from
external module:
```
$ objdump -rdS T15723B.o
0000000000000028 <T15723B_test_info>:
  28:   48 8d 45 f0             lea    -0x10(%rbp),%rax
  2c:   4c 39 f8                cmp    %r15,%rax
  2f:   72 70                   jb     a1 <T15723B_test_info+0x79>
  31:   48 83 ec 08             sub    $0x8,%rsp
  35:   48 8d 35 00 00 00 00    lea    0x0(%rip),%rsi        # 3c
<T15723B_test_info+0x14>
                        38: R_X86_64_PC32
T15723B_test1_EXPR_cc-0x4
  3c:   49 8b bd 60 03 00 00    mov    0x360(%r13),%rdi
  43:   31 c0                   xor    %eax,%eax
  45:   e8 00 00 00 00          callq  4a <T15723B_test_info+0x22>
                        46: R_X86_64_PLT32      pushCostCentre-0x4
  4a:   48 83 c4 08             add    $0x8,%rsp
  4e:   48 ff 40 30             incq   0x30(%rax)
  52:   49 89 85 60 03 00 00    mov    %rax,0x360(%r13)
  59:   48 83 ec 08             sub    $0x8,%rsp
  5d:   49 8b bd 60 03 00 00    mov    0x360(%r13),%rdi
  64:   48 8b 35 00 00 00 00    mov    0x0(%rip),%rsi        # 6b
<T15723B_test_info+0x43>
                        67: R_X86_64_GOTPCREL   T15723A_foo1_EXPR_cc-0x4
  6b:   31 c0                   xor    %eax,%eax
  6d:   e8 00 00 00 00          callq  72 <T15723B_test_info+0x4a>
                        6e: R_X86_64_PLT32      pushCostCentre-0x4
  72:   48 83 c4 08             add    $0x8,%rsp
  76:   48 ff 40 30             incq   0x30(%rax)
```

Reviewers: simonmar, bgamari

Reviewed By: simonmar

Subscribers: rwbarton, carter

GHC Trac Issues: #15723

Differential Revision: https://phabricator.haskell.org/D5214

1 files changed, 11 insertions, 4 deletions

diff --git a/compiler/cmm/CLabel.hs b/compiler/cmm/CLabel.hs
index f07abebf50..dbb92e5f41 100644
--- a/compiler/cmm/CLabel.hs
+++ b/compiler/cmm/CLabel.hs
@@ -1019,7 +1019,7 @@ labelDynamic dflags this_mod lbl =
   case lbl of
    -- is the RTS in a DLL or not?
    RtsLabel _ ->
-     (gopt Opt_ExternalDynamicRefs dflags) && (this_pkg /= rtsUnitId)
+     externalDynamicRefs && (this_pkg /= rtsUnitId)
 
    IdLabel n _ _ ->
      isDllName dflags this_mod n
@@ -1028,7 +1028,7 @@ labelDynamic dflags this_mod lbl =
    -- its own shared library.
    CmmLabel pkg _ _
     | os == OSMinGW32 ->
-       (gopt Opt_ExternalDynamicRefs dflags) && (this_pkg /= pkg)
+       externalDynamicRefs && (this_pkg /= pkg)
     | otherwise ->
        gopt Opt_ExternalDynamicRefs dflags
 
@@ -1048,19 +1048,26 @@ labelDynamic dflags this_mod lbl =
             -- When compiling in the "dyn" way, each package is to be
             -- linked into its own DLL.
             ForeignLabelInPackage pkgId ->
-                (gopt Opt_ExternalDynamicRefs dflags) && (this_pkg /= pkgId)
+                externalDynamicRefs && (this_pkg /= pkgId)
 
        else -- On Mac OS X and on ELF platforms, false positives are OK,
             -- so we claim that all foreign imports come from dynamic
             -- libraries
             True
 
+   CC_Label cc ->
+     externalDynamicRefs && not (ccFromThisModule cc this_mod)
+
+   -- CCS_Label always contains a CostCentre defined in the current module
+   CCS_Label _ -> False
+
    HpcTicksLabel m ->
-     (gopt Opt_ExternalDynamicRefs dflags) && this_mod /= m
+     externalDynamicRefs && this_mod /= m
 
    -- Note that DynamicLinkerLabels do NOT require dynamic linking themselves.
    _                 -> False
   where
+    externalDynamicRefs = gopt Opt_ExternalDynamicRefs dflags
     os = platformOS (targetPlatform dflags)
     this_pkg = moduleUnitId this_mod