Enable USE_INLINE_SRT_FIELD on ARM64

It was previously disabled because of:
- a confusion about "SRT inlining" (see removed comment in this commit)
- a linker bug (overflow) in the handling of ARM64_RELOC_SUBTRACTOR
  relocation: fixed by a previous commit.

2 files changed, 3 insertions, 16 deletions

diff --git a/compiler/GHC/Cmm/Info/Build.hs b/compiler/GHC/Cmm/Info/Build.hs
index 4d5b277f52..5a3b22f8b8 100644
--- a/compiler/GHC/Cmm/Info/Build.hs
+++ b/compiler/GHC/Cmm/Info/Build.hs
@@ -167,16 +167,6 @@ Requires:
   - 64-bit architecture
   - small memory model
 
-Currently it is only enabled on x86_64 with TABLES_NEXT_TO_CODE.
-
-It is claimed that MachO doesn't support it due to #15169. However I believe
-that two kinds of SRT inlining have been confused:
-- inlining the SRT offset in the info->srt field
-  - should always be fine
-- inlining singleton SRT (i.e. SRT containing one reference)
-  - this can lead to a relative reference to an object external to the
-    compilation unit (c.f. #15169)
-
 We optimise the info table representation further.  The offset to the SRT can
 be stored in 32 bits (all code lives within a 2GB region in x86_64's small
 memory model), so we can save a word in the info table by storing the
@@ -1162,7 +1152,8 @@ oneSRT cfg staticFuns lbls caf_lbls isCAF cafs static_data_env = do
           not (labelDynamic this_mod platform (cmmExternalDynamicRefs cfg) lbl)
 
           -- MachO relocations can't express offsets between compilation units at
-          -- all, so we are always forced to build a singleton SRT in this case.
+          -- all, so we are always forced to build a singleton SRT in this case
+          -- (cf #15169)
             && (not (osMachOTarget $ platformOS $ profilePlatform profile)
                || isLocalCLabel this_mod lbl) -> do
 
diff --git a/rts/include/rts/storage/InfoTables.h b/rts/include/rts/storage/InfoTables.h
index 39423a3f9f..77f45fb533 100644
--- a/rts/include/rts/storage/InfoTables.h
+++ b/rts/include/rts/storage/InfoTables.h
@@ -156,16 +156,12 @@ typedef union {
 } StgClosureInfo;
 
 
-#if defined(x86_64_HOST_ARCH)
-#define SMALL_MEMORY_MODEL
-#endif
-
 // This is where we choose how to represent the SRT location in the info
 // table.  See the section "Referring to an SRT from the info table" in
 // Note [SRTs] in GHC.Cmm.Info.Build.
 //
 // Specifically we define one of the following:
-#if WORD_SIZE_IN_BITS == 64 && defined(SMALL_MEMORY_MODEL) && defined(TABLES_NEXT_TO_CODE)
+#if WORD_SIZE_IN_BITS == 64 && defined(TABLES_NEXT_TO_CODE)
 // On 64-bit platforms using the small memory model we can fit a pointer
 // offset in half a word, so put the SRT offset in the info->srt field
 // directly.