[commit: ghc] master: llvm backend: Put string constants in .rodata.str.* sections (#13265) (90009cf)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/90009cf62bcebf875e68af625dbdbfc3c2f71717/ghc

>---------------------------------------------------------------

commit 90009cf62bcebf875e68af625dbdbfc3c2f71717
Author: Reid Barton <rwbarton at gmail.com>
Date:   Thu Mar 9 10:42:49 2017 -0500

    llvm backend: Put string constants in .rodata.str.* sections (#13265)
    
    The .cstring.* sections don't get merged by the linker (bfd or gold).
    That's bad, and especially bad in #13265 where it caused the number of
    sections to exceed what is apparently an internal limit in ld.bfd.
    
    Test Plan:
    I can only test this on Linux, and I am guessing at what
    the correct behavior is on Mac OS and Windows (and AIX I suppose).
    Testers on other platforms would be much appreciated, though I
    understand that the LLVM backend is broken on Mac OS currently for
    other reasons (#13378).
    
    Reviewers: olsner, austin, xnyhps, bgamari
    
    Reviewed By: bgamari
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D3282


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90009cf62bcebf875e68af625dbdbfc3c2f71717
 compiler/llvmGen/LlvmCodeGen/Data.hs | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/compiler/llvmGen/LlvmCodeGen/Data.hs b/compiler/llvmGen/LlvmCodeGen/Data.hs
index 0f0ca6e..9bb5a75 100644
--- a/compiler/llvmGen/LlvmCodeGen/Data.hs
+++ b/compiler/llvmGen/LlvmCodeGen/Data.hs
@@ -16,6 +16,7 @@ import BlockId
 import CLabel
 import Cmm
 import DynFlags
+import Platform
 
 import FastString
 import Outputable
@@ -46,8 +47,11 @@ genLlvmData (sec, Statics lbl xs) = do
         struct         = Just $ LMStaticStruc static tyAlias
         link           = if (externallyVisibleCLabel lbl)
                             then ExternallyVisible else Internal
+        align          = case sec of
+                            Section CString _ -> Just 1
+                            _                 -> Nothing
         const          = if isSecConstant sec then Constant else Global
-        varDef         = LMGlobalVar label tyAlias link lmsec Nothing const
+        varDef         = LMGlobalVar label tyAlias link lmsec align const
         globDef        = LMGlobal varDef struct
 
     return ([globDef], [tyAlias])
@@ -65,15 +69,17 @@ isSecConstant (Section t _) = case t of
     (OtherSection _)        -> False
 
 -- | Format the section type part of a Cmm Section
-llvmSectionType :: SectionType -> FastString
-llvmSectionType t = case t of
+llvmSectionType :: Platform -> SectionType -> FastString
+llvmSectionType p t = case t of
     Text                    -> fsLit ".text"
     ReadOnlyData            -> fsLit ".rodata"
     RelocatableReadOnlyData -> fsLit ".data.rel.ro"
     ReadOnlyData16          -> fsLit ".rodata.cst16"
     Data                    -> fsLit ".data"
     UninitialisedData       -> fsLit ".bss"
-    CString                 -> fsLit ".cstring"
+    CString                 -> case platformOS p of
+                                 OSMinGW32 -> fsLit ".rdata"
+                                 _         -> fsLit ".rodata.str"
     (OtherSection _)        -> panic "llvmSectionType: unknown section type"
 
 -- | Format a Cmm Section into a LLVM section name
@@ -81,11 +87,12 @@ llvmSection :: Section -> LlvmM LMSection
 llvmSection (Section t suffix) = do
   dflags <- getDynFlags
   let splitSect = gopt Opt_SplitSections dflags
+      platform  = targetPlatform dflags
   if not splitSect
   then return Nothing
   else do
     lmsuffix <- strCLabel_llvm suffix
-    return (Just (concatFS [llvmSectionType t, fsLit ".", lmsuffix]))
+    return (Just (concatFS [llvmSectionType platform t, fsLit ".", lmsuffix]))
 
 -- ----------------------------------------------------------------------------
 -- * Generate static data