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.

8 files changed, 50 insertions, 58 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;
+    }
+}
diff --git a/src/glibc.zig b/src/glibc.zig
index 2e42cef519..0c27872720 100644
--- a/src/glibc.zig
+++ b/src/glibc.zig
@@ -271,7 +271,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                 try lib_path(comp, arena, lib_libc_glibc ++ "include" ++ path.sep_str ++ "libc-symbols.h"),
                 "-DTOP_NAMESPACE=glibc",
                 "-DASSEMBLER",
-                "-g",
                 "-Wa,--noexecstack",
             });
             return comp.build_crt_file("crti", .Obj, &[1]Compilation.CSourceFile{
@@ -291,7 +290,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                 try lib_path(comp, arena, lib_libc_glibc ++ "include" ++ path.sep_str ++ "libc-symbols.h"),
                 "-DTOP_NAMESPACE=glibc",
                 "-DASSEMBLER",
-                "-g",
                 "-Wa,--noexecstack",
             });
             return comp.build_crt_file("crtn", .Obj, &[1]Compilation.CSourceFile{
@@ -317,7 +315,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                     "-DSHARED",
                     "-DTOP_NAMESPACE=glibc",
                     "-DASSEMBLER",
-                    "-g",
                     "-Wa,--noexecstack",
                 });
                 break :blk .{
@@ -337,7 +334,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                     "-DMODULE_NAME=libc",
                     "-DTOP_NAMESPACE=glibc",
                     "-DASSEMBLER",
-                    "-g",
                     "-Wa,--noexecstack",
                 });
                 break :blk .{
@@ -372,8 +368,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                 try args.appendSlice(&[_][]const u8{
                     "-std=gnu11",
                     "-fgnu89-inline",
-                    "-g",
-                    "-O2",
                     "-fmerge-all-constants",
                     "-fno-stack-protector",
                     "-fmath-errno",
@@ -409,8 +403,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                 try args.appendSlice(&[_][]const u8{
                     "-std=gnu11",
                     "-fgnu89-inline",
-                    "-g",
-                    "-O2",
                     "-fmerge-all-constants",
                     "-fno-stack-protector",
                     "-fmath-errno",
@@ -939,13 +931,13 @@ fn buildSharedLib(
         .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,
         .want_tsan = false,
         .emit_h = null,
-        .strip = comp.bin_file.options.strip,
+        .strip = comp.compilerRtStrip(),
         .is_native_os = false,
         .is_native_abi = false,
         .self_exe_path = comp.self_exe_path,
diff --git a/src/libcxx.zig b/src/libcxx.zig
index 47bf93dee3..e79a0106e9 100644
--- a/src/libcxx.zig
+++ b/src/libcxx.zig
@@ -138,7 +138,6 @@ pub fn buildLibCXX(comp: *Compilation) !void {
         try cflags.append("-I");
         try cflags.append(cxxabi_include_path);
 
-        try cflags.append("-O3");
         if (target_util.supports_fpic(target)) {
             try cflags.append("-fPIC");
         }
@@ -164,7 +163,7 @@ pub fn buildLibCXX(comp: *Compilation) !void {
         .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(),
         .link_mode = link_mode,
         .want_sanitize_c = false,
         .want_stack_check = false,
@@ -173,7 +172,7 @@ pub fn buildLibCXX(comp: *Compilation) !void {
         .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,
@@ -256,16 +255,12 @@ pub fn buildLibCXXABI(comp: *Compilation) !void {
         try cflags.append("-I");
         try cflags.append(cxx_include_path);
 
-        try cflags.append("-O3");
-        try cflags.append("-DNDEBUG");
         if (target_util.supports_fpic(target)) {
             try cflags.append("-fPIC");
         }
         try cflags.append("-nostdinc++");
         try cflags.append("-fstrict-aliasing");
         try cflags.append("-funwind-tables");
-        try cflags.append("-D_DEBUG");
-        try cflags.append("-UNDEBUG");
         try cflags.append("-std=c++11");
 
         c_source_files[i] = .{
@@ -285,7 +280,7 @@ pub fn buildLibCXXABI(comp: *Compilation) !void {
         .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(),
         .link_mode = link_mode,
         .want_sanitize_c = false,
         .want_stack_check = false,
@@ -294,7 +289,7 @@ pub fn buildLibCXXABI(comp: *Compilation) !void {
         .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,
diff --git a/src/libtsan.zig b/src/libtsan.zig
index ecf15693e1..d126d7313a 100644
--- a/src/libtsan.zig
+++ b/src/libtsan.zig
@@ -43,8 +43,6 @@ pub fn buildTsan(comp: *Compilation) !void {
         try cflags.append("-I");
         try cflags.append(tsan_include_path);
 
-        try cflags.append("-O3");
-        try cflags.append("-DNDEBUG");
         try cflags.append("-nostdinc++");
         try cflags.append("-fvisibility-inlines-hidden");
         try cflags.append("-std=c++14");
@@ -67,8 +65,6 @@ pub fn buildTsan(comp: *Compilation) !void {
         try cflags.append("-I");
         try cflags.append(tsan_include_path);
 
-        try cflags.append("-O3");
-        try cflags.append("-DNDEBUG");
         try cflags.append("-nostdinc++");
         try cflags.append("-fvisibility-inlines-hidden");
         try cflags.append("-std=c++14");
@@ -110,8 +106,6 @@ pub fn buildTsan(comp: *Compilation) !void {
         try cflags.append("-I");
         try cflags.append(sanitizer_common_include_path);
 
-        try cflags.append("-O3");
-        try cflags.append("-DNDEBUG");
         try cflags.append("-nostdinc++");
         try cflags.append("-fvisibility-inlines-hidden");
         try cflags.append("-std=c++14");
@@ -136,8 +130,6 @@ pub fn buildTsan(comp: *Compilation) !void {
         try cflags.append("-I");
         try cflags.append(sanitizer_common_include_path);
 
-        try cflags.append("-O3");
-        try cflags.append("-DNDEBUG");
         try cflags.append("-nostdinc++");
         try cflags.append("-fvisibility-inlines-hidden");
         try cflags.append("-std=c++14");
@@ -158,8 +150,6 @@ pub fn buildTsan(comp: *Compilation) !void {
         try cflags.append("-I");
         try cflags.append(tsan_include_path);
 
-        try cflags.append("-O3");
-        try cflags.append("-DNDEBUG");
         try cflags.append("-nostdinc++");
         try cflags.append("-fvisibility-inlines-hidden");
         try cflags.append("-std=c++14");
@@ -188,8 +178,6 @@ pub fn buildTsan(comp: *Compilation) !void {
         try cflags.append("-I");
         try cflags.append(tsan_include_path);
 
-        try cflags.append("-O3");
-        try cflags.append("-DNDEBUG");
         try cflags.append("-nostdinc++");
         try cflags.append("-fvisibility-inlines-hidden");
         try cflags.append("-std=c++14");
@@ -218,7 +206,7 @@ pub fn buildTsan(comp: *Compilation) !void {
         .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(),
         .link_mode = link_mode,
         .want_sanitize_c = false,
         .want_stack_check = false,
@@ -227,7 +215,7 @@ pub fn buildTsan(comp: *Compilation) !void {
         .want_pic = true,
         .want_pie = true,
         .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,
diff --git a/src/libunwind.zig b/src/libunwind.zig
index 057663a44b..7710b1aa77 100644
--- a/src/libunwind.zig
+++ b/src/libunwind.zig
@@ -104,7 +104,7 @@ pub fn buildStaticLib(comp: *Compilation) !void {
         .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(),
         .link_mode = link_mode,
         .want_sanitize_c = false,
         .want_stack_check = false,
@@ -113,7 +113,7 @@ pub fn buildStaticLib(comp: *Compilation) !void {
         .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,
diff --git a/src/mingw.zig b/src/mingw.zig
index 8c819627ba..a9e275434f 100644
--- a/src/mingw.zig
+++ b/src/mingw.zig
@@ -91,8 +91,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                     "-D_CRTBLD",
                     "-D_WIN32_WINNT=0x0f00",
                     "-D__MSVCRT_VERSION__=0x700",
-                    "-g",
-                    "-O2",
                 });
                 c_source_files[i] = .{
                     .src_path = try comp.zig_lib_directory.join(arena, &[_][]const u8{
@@ -119,9 +117,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
 
                 "-isystem",
                 try comp.zig_lib_directory.join(arena, &[_][]const u8{ "libc", "include", "any-windows-any" }),
-
-                "-g",
-                "-O2",
             });
             var c_source_files = std.ArrayList(Compilation.CSourceFile).init(arena);
 
@@ -167,8 +162,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                 "-D_CRTBLD",
                 "-D_WIN32_WINNT=0x0f00",
                 "-D__MSVCRT_VERSION__=0x700",
-                "-g",
-                "-O2",
 
                 "-isystem",
                 try comp.zig_lib_directory.join(arena, &[_][]const u8{ "libc", "include", "any-windows-any" }),
@@ -233,8 +226,6 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                 "-D_CRTBLD",
                 "-D_WIN32_WINNT=0x0f00",
                 "-D__MSVCRT_VERSION__=0x700",
-                "-g",
-                "-O2",
 
                 "-isystem",
                 try comp.zig_lib_directory.join(arena, &[_][]const u8{
diff --git a/src/musl.zig b/src/musl.zig
index 6680eabb03..f67fe90add 100644
--- a/src/musl.zig
+++ b/src/musl.zig
@@ -203,13 +203,13 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
                 .thread_pool = comp.thread_pool,
                 .libc_installation = comp.bin_file.options.libc_installation,
                 .emit_bin = Compilation.EmitLoc{ .directory = null, .basename = "libc.so" },
-                .optimize_mode = comp.bin_file.options.optimize_mode,
+                .optimize_mode = comp.compilerRtOptMode(),
                 .want_sanitize_c = false,
                 .want_stack_check = false,
                 .want_valgrind = false,
                 .want_tsan = false,
                 .emit_h = null,
-                .strip = comp.bin_file.options.strip,
+                .strip = comp.compilerRtStrip(),
                 .is_native_os = false,
                 .is_native_abi = false,
                 .self_exe_path = comp.self_exe_path,
diff --git a/src/target.zig b/src/target.zig
index 9749675a89..b3c83c76d8 100644
--- a/src/target.zig
+++ b/src/target.zig
@@ -344,3 +344,11 @@ pub fn is_libcpp_lib_name(target: std.Target, name: []const u8) bool {
 pub fn hasDebugInfo(target: std.Target) bool {
     return !target.cpu.arch.isWasm();
 }
+
+pub fn defaultCompilerRtOptimizeMode(target: std.Target) std.builtin.Mode {
+    if (target.cpu.arch.isWasm() and target.os.tag == .freestanding) {
+        return .ReleaseSmall;
+    } else {
+        return .ReleaseFast;
+    }
+}