stage2: re-use compiler runtime libs across opt modes and strip flag

Previously Zig would need to recompile runtime libs if you changed the
values of --strip or -O. Now, unless the `debug_compiler_runtime_libs`
flag is set (which is currently not exposed to the CLI), Zig will always
choose ReleaseFast or ReleaseSmall for compiler runtime libraries.

When the main application chooses ReleaseFast or ReleaseSmall, that
value is propagated to compiler runtime libraries. Otherwise a decision
is made based on the target, which is currently ReleaseSmall for
freestanding WebAssembly and ReleaseFast for everything else.

Ultimately the purpose of this commit is to have Debug and ReleaseSafe
builds of applications still get optimized builds of, e.g. libcxx and
libunwind, as well as to spend less time unnecessarily rebuilding compiler
runtime libraries.

1 files changed, 30 insertions, 12 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index 010ac96b6f..885ecbb95c 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -131,6 +131,7 @@ mutex: std.Mutex = .{},
 test_filter: ?[]const u8,
 test_name_prefix: ?[]const u8,
 test_evented_io: bool,
+debug_compiler_runtime_libs: bool,
 
 emit_asm: ?EmitLoc,
 emit_llvm_ir: ?EmitLoc,
@@ -429,6 +430,7 @@ pub const InitOptions = struct {
     verbose_llvm_cpu_features: bool = false,
     is_test: bool = false,
     test_evented_io: bool = false,
+    debug_compiler_runtime_libs: bool = false,
     /// Normally when you create a `Compilation`, Zig will automatically build
     /// and link in required dependencies, such as compiler-rt and libc. When
     /// building such dependencies themselves, this flag must be set to avoid
@@ -1025,6 +1027,7 @@ pub fn create(gpa: *Allocator, options: InitOptions) !*Compilation {
             .test_filter = options.test_filter,
             .test_name_prefix = options.test_name_prefix,
             .test_evented_io = options.test_evented_io,
+            .debug_compiler_runtime_libs = options.debug_compiler_runtime_libs,
             .work_queue_wait_group = undefined,
         };
         break :comp comp;
@@ -2891,14 +2894,6 @@ fn buildOutputFromZig(
         .directory = null, // Put it in the cache directory.
         .basename = bin_basename,
     };
-    const optimize_mode: std.builtin.Mode = blk: {
-        if (comp.bin_file.options.is_test)
-            break :blk comp.bin_file.options.optimize_mode;
-        switch (comp.bin_file.options.optimize_mode) {
-            .Debug, .ReleaseFast, .ReleaseSafe => break :blk .ReleaseFast,
-            .ReleaseSmall => break :blk .ReleaseSmall,
-        }
-    };
     const sub_compilation = try Compilation.create(comp.gpa, .{
         .global_cache_directory = comp.global_cache_directory,
         .local_cache_directory = comp.global_cache_directory,
@@ -2910,7 +2905,7 @@ fn buildOutputFromZig(
         .thread_pool = comp.thread_pool,
         .libc_installation = comp.bin_file.options.libc_installation,
         .emit_bin = emit_bin,
-        .optimize_mode = optimize_mode,
+        .optimize_mode = comp.compilerRtOptMode(),
         .link_mode = .Static,
         .function_sections = true,
         .want_sanitize_c = false,
@@ -2920,7 +2915,7 @@ fn buildOutputFromZig(
         .want_pic = comp.bin_file.options.pic,
         .want_pie = comp.bin_file.options.pie,
         .emit_h = null,
-        .strip = comp.bin_file.options.strip,
+        .strip = comp.compilerRtStrip(),
         .is_native_os = comp.bin_file.options.is_native_os,
         .is_native_abi = comp.bin_file.options.is_native_abi,
         .self_exe_path = comp.self_exe_path,
@@ -3289,7 +3284,7 @@ pub fn build_crt_file(
         .thread_pool = comp.thread_pool,
         .libc_installation = comp.bin_file.options.libc_installation,
         .emit_bin = emit_bin,
-        .optimize_mode = comp.bin_file.options.optimize_mode,
+        .optimize_mode = comp.compilerRtOptMode(),
         .want_sanitize_c = false,
         .want_stack_check = false,
         .want_valgrind = false,
@@ -3297,7 +3292,7 @@ pub fn build_crt_file(
         .want_pic = comp.bin_file.options.pic,
         .want_pie = comp.bin_file.options.pie,
         .emit_h = null,
-        .strip = comp.bin_file.options.strip,
+        .strip = comp.compilerRtStrip(),
         .is_native_os = comp.bin_file.options.is_native_os,
         .is_native_abi = comp.bin_file.options.is_native_abi,
         .self_exe_path = comp.self_exe_path,
@@ -3344,3 +3339,26 @@ pub fn stage1AddLinkLib(comp: *Compilation, lib_name: []const u8) !void {
         });
     }
 }
+
+/// This decides the optimization mode for all zig-provided libraries, including
+/// compiler-rt, libcxx, libc, libunwind, etc.
+pub fn compilerRtOptMode(comp: Compilation) std.builtin.Mode {
+    if (comp.debug_compiler_runtime_libs) {
+        return comp.bin_file.options.optimize_mode;
+    }
+    switch (comp.bin_file.options.optimize_mode) {
+        .Debug, .ReleaseSafe => return target_util.defaultCompilerRtOptimizeMode(comp.getTarget()),
+        .ReleaseFast => return .ReleaseFast,
+        .ReleaseSmall => return .ReleaseSmall,
+    }
+}
+
+/// This decides whether to strip debug info for all zig-provided libraries, including
+/// compiler-rt, libcxx, libc, libunwind, etc.
+pub fn compilerRtStrip(comp: Compilation) bool {
+    if (comp.debug_compiler_runtime_libs) {
+        return comp.bin_file.options.strip;
+    } else {
+        return true;
+    }
+}