add LTO support

The CLI gains -flto and -fno-lto options to override the default.
However, the cool thing about this is that the defaults are great! In
general when you use build-exe in release mode, Zig will enable LTO if
it would work and it would help.

zig cc supports detecting and honoring the -flto and -fno-lto flags as
well. The linkWithLld functions are improved to all be the same with
regards to copying the artifact instead of trying to pass single objects
through LLD with -r. There is possibly a future improvement here as
well; see the respective TODOs.

stage1 is updated to support outputting LLVM bitcode instead of machine
code when lto is enabled. This allows LLVM to optimize across the Zig and
C/C++ code boundary.

closes #2845

1 files changed, 7 insertions, 1 deletions

diff --git a/src/codegen/llvm/bindings.zig b/src/codegen/llvm/bindings.zig
index 8774260a08..6474957b1c 100644
--- a/src/codegen/llvm/bindings.zig
+++ b/src/codegen/llvm/bindings.zig
@@ -243,7 +243,13 @@ pub const TargetMachine = opaque {
     extern fn LLVMDisposeTargetMachine(T: *const TargetMachine) void;
 
     pub const emitToFile = LLVMTargetMachineEmitToFile;
-    extern fn LLVMTargetMachineEmitToFile(*const TargetMachine, M: *const Module, Filename: [*:0]const u8, codegen: CodeGenFileType, ErrorMessage: *[*:0]const u8) LLVMBool;
+    extern fn LLVMTargetMachineEmitToFile(
+        *const TargetMachine,
+        M: *const Module,
+        Filename: [*:0]const u8,
+        codegen: CodeGenFileType,
+        ErrorMessage: *[*:0]const u8,
+    ) LLVMBool;
 };
 
 pub const CodeMode = extern enum {