From 3c9bf508d04734c5b5e2467b4fddeb2de29f8dba Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Sat, 9 Aug 2014 12:43:45 -0400
Subject: [PATCH] optimize position independent code in executables

Position independent code has fewer requirements in executables, so pass
the appropriate flag to LLVM in order to allow more optimization. At the
moment this means faster thread-local storage.
---
 src/librustc/back/link.rs    | 5 +++++
 src/librustc_llvm/lib.rs     | 2 ++
 src/rustllvm/PassWrapper.cpp | 2 ++
 3 files changed, 9 insertions(+)

diff --git a/src/librustc/back/link.rs b/src/librustc/back/link.rs
index 7c9844dbe33fb..47275f386e5e4 100644
--- a/src/librustc/back/link.rs
+++ b/src/librustc/back/link.rs
@@ -197,6 +197,10 @@ pub mod write {
                              (sess.targ_cfg.os == abi::OsMacos &&
                               sess.targ_cfg.arch == abi::X86_64);
 
+            let any_library = sess.crate_types.borrow().iter().any(|ty| {
+                *ty != config::CrateTypeExecutable
+            });
+
             // OSX has -dead_strip, which doesn't rely on ffunction_sections
             // FIXME(#13846) this should be enabled for windows
             let ffunction_sections = sess.targ_cfg.os != abi::OsMacos &&
@@ -249,6 +253,7 @@ pub mod write {
                             true /* EnableSegstk */,
                             use_softfp,
                             no_fp_elim,
+                            !any_library && reloc_model == llvm::RelocPIC,
                             ffunction_sections,
                             fdata_sections,
                         )
diff --git a/src/librustc_llvm/lib.rs b/src/librustc_llvm/lib.rs
index 1ac0aee85d4d9..13a7ec743a884 100644
--- a/src/librustc_llvm/lib.rs
+++ b/src/librustc_llvm/lib.rs
@@ -340,6 +340,7 @@ pub enum CodeGenOptLevel {
     CodeGenLevelAggressive = 3,
 }
 
+#[deriving(PartialEq)]
 #[repr(C)]
 pub enum RelocMode {
     RelocDefault = 0,
@@ -1869,6 +1870,7 @@ extern {
                                        EnableSegstk: bool,
                                        UseSoftFP: bool,
                                        NoFramePointerElim: bool,
+                                       PositionIndependentExecutable: bool,
                                        FunctionSections: bool,
                                        DataSections: bool) -> TargetMachineRef;
     pub fn LLVMRustDisposeTargetMachine(T: TargetMachineRef);
diff --git a/src/rustllvm/PassWrapper.cpp b/src/rustllvm/PassWrapper.cpp
index 195b044ccdcef..6409491272731 100644
--- a/src/rustllvm/PassWrapper.cpp
+++ b/src/rustllvm/PassWrapper.cpp
@@ -71,6 +71,7 @@ LLVMRustCreateTargetMachine(const char *triple,
                             bool EnableSegmentedStacks,
                             bool UseSoftFloat,
                             bool NoFramePointerElim,
+                            bool PositionIndependentExecutable,
                             bool FunctionSections,
                             bool DataSections) {
     std::string Error;
@@ -83,6 +84,7 @@ LLVMRustCreateTargetMachine(const char *triple,
     }
 
     TargetOptions Options;
+    Options.PositionIndependentExecutable = PositionIndependentExecutable;
     Options.NoFramePointerElim = NoFramePointerElim;
 #if LLVM_VERSION_MINOR < 5
     Options.EnableSegmentedStacks = EnableSegmentedStacks;