Implement function-sections for Haskell code, #8405

This adds a flag -split-sections that does similar things to
-split-objs, but using sections in single object files instead of
relying on the Satanic Splitter and other abominations. This is very
similar to the GCC flags -ffunction-sections and -fdata-sections.

The --gc-sections linker flag, which allows unused sections to actually
be removed, is added to all link commands (if the linker supports it) so
that space savings from having base compiled with sections can be
realized.

Supported both in LLVM and the native code-gen, in theory for all
architectures, but really tested on x86 only.

In the GHC build, a new SplitSections variable enables -split-sections
for relevant parts of the build.

Test Plan: validate with both settings of SplitSections

Reviewers: dterei, Phyx, austin, simonmar, thomie, bgamari

Reviewed By: simonmar, thomie, bgamari

Subscribers: hsyl20, erikd, kgardas, thomie

Differential Revision: https://phabricator.haskell.org/D1242

GHC Trac Issues: #8405

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/codeGen/StgCmm.hs b/compiler/codeGen/StgCmm.hs
index efc89fe04a..b0dd9b11b8 100644
--- a/compiler/codeGen/StgCmm.hs
+++ b/compiler/codeGen/StgCmm.hs
@@ -194,7 +194,8 @@ mkModuleInit cost_centre_info this_mod hpc_info
         ; initCostCentres cost_centre_info
             -- For backwards compatibility: user code may refer to this
             -- label for calling hs_add_root().
-        ; emitDecl (CmmData Data (Statics (mkPlainModuleInitLabel this_mod) []))
+        ; let lbl = mkPlainModuleInitLabel this_mod
+        ; emitDecl (CmmData (Section Data lbl) (Statics lbl []))
         }