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/write.rs

@@ -34,7 +34,6 @@ use std::sync::{Arc, Mutex};
 use std::task::TaskBuilder;
 use libc::{c_uint, c_int, c_void};
 
-
 #[deriving(Clone, PartialEq, PartialOrd, Ord, Eq)]
 pub enum OutputType {
     OutputTypeBitcode,
@@ -44,7 +43,6 @@ pub enum OutputType {
     OutputTypeExe,
 }
 
-
 pub fn llvm_err(handler: &diagnostic::Handler, msg: String) -> ! {
     unsafe {
         let cstr = llvm::LLVMRustGetLastError();
@@ -202,6 +200,10 @@ fn create_target_machine(sess: &Session) -> TargetMachineRef {
                      (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 &&
@@ -240,6 +242,7 @@ fn create_target_machine(sess: &Session) -> TargetMachineRef {
                         true /* EnableSegstk */,
                         use_softfp,
                         no_fp_elim,
+                        !any_library && reloc_model == llvm::RelocPIC,
                         ffunction_sections,
                         fdata_sections,
                     )

src/librustc_llvm/lib.rs

@@ -353,6 +353,7 @@ pub enum CodeGenOptLevel {
     CodeGenLevelAggressive = 3,
 }
 
+#[deriving(PartialEq)]
 #[repr(C)]
 pub enum RelocMode {
     RelocDefault = 0,
@@ -1907,6 +1908,7 @@ extern {
                                        EnableSegstk: bool,
                                        UseSoftFP: bool,
                                        NoFramePointerElim: bool,
+                                       PositionIndependentExecutable: bool,
                                        FunctionSections: bool,
                                        DataSections: bool) -> TargetMachineRef;
     pub fn LLVMRustDisposeTargetMachine(T: TargetMachineRef);

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;