Disable LTO by default + some LTO fixes

lib/compiler_rt/arm.zig

@@ -15,11 +15,11 @@ comptime {
             @export(&__aeabi_unwind_cpp_pr1, .{ .name = "__aeabi_unwind_cpp_pr1", .linkage = common.linkage, .visibility = common.visibility });
             @export(&__aeabi_unwind_cpp_pr2, .{ .name = "__aeabi_unwind_cpp_pr2", .linkage = common.linkage, .visibility = common.visibility });
 
-            @export(&__aeabi_ldivmod, .{ .name = if (target.isMinGW()) "__rt_sdiv64" else "__aeabi_ldivmod", .linkage = common.linkage, .visibility = common.visibility });
-            @export(&__aeabi_uldivmod, .{ .name = if (target.isMinGW()) "__rt_udiv64" else "__aeabi_uldivmod", .linkage = common.linkage, .visibility = common.visibility });
+            @export(&__aeabi_ldivmod, .{ .name = if (common.want_windows_arm_abi) "__rt_sdiv64" else "__aeabi_ldivmod", .linkage = common.linkage, .visibility = common.visibility });
+            @export(&__aeabi_uldivmod, .{ .name = if (common.want_windows_arm_abi) "__rt_udiv64" else "__aeabi_uldivmod", .linkage = common.linkage, .visibility = common.visibility });
 
-            @export(&__aeabi_idivmod, .{ .name = if (target.isMinGW()) "__rt_sdiv" else "__aeabi_idivmod", .linkage = common.linkage, .visibility = common.visibility });
-            @export(&__aeabi_uidivmod, .{ .name = if (target.isMinGW()) "__rt_udiv" else "__aeabi_uidivmod", .linkage = common.linkage, .visibility = common.visibility });
+            @export(&__aeabi_idivmod, .{ .name = if (common.want_windows_arm_abi) "__rt_sdiv" else "__aeabi_idivmod", .linkage = common.linkage, .visibility = common.visibility });
+            @export(&__aeabi_uidivmod, .{ .name = if (common.want_windows_arm_abi) "__rt_udiv" else "__aeabi_uidivmod", .linkage = common.linkage, .visibility = common.visibility });
 
             @export(&__aeabi_memcpy, .{ .name = "__aeabi_memcpy", .linkage = common.linkage, .visibility = common.visibility });
             @export(&__aeabi_memcpy4, .{ .name = "__aeabi_memcpy4", .linkage = common.linkage, .visibility = common.visibility });
@@ -136,11 +136,14 @@ pub fn __aeabi_uidivmod() callconv(.Naked) void {
         \\ push {lr}
         \\ sub sp, #4
         \\ mov r2, sp
-        \\ bl  __udivmodsi4
+        \\ bl  %[__udivmodsi4]
         \\ ldr r1, [sp]
         \\ add sp, #4
         \\ pop {pc}
-        ::: "memory");
+        :
+        : [__udivmodsi4] "X" (&__udivmodsi4),
+        : "memory"
+    );
     unreachable;
 }
 
@@ -152,12 +155,15 @@ pub fn __aeabi_uldivmod() callconv(.Naked) void {
         \\ sub sp, #16
         \\ add r4, sp, #8
         \\ str r4, [sp]
-        \\ bl  __udivmoddi4
+        \\ bl  %[__udivmoddi4]
         \\ ldr r2, [sp, #8]
         \\ ldr r3, [sp, #12]
         \\ add sp, #16
         \\ pop {r4, pc}
-        ::: "memory");
+        :
+        : [__udivmoddi4] "X" (&__udivmoddi4),
+        : "memory"
+    );
     unreachable;
 }
 
@@ -168,11 +174,14 @@ pub fn __aeabi_idivmod() callconv(.Naked) void {
         \\ push {lr}
         \\ sub sp, #4
         \\ mov r2, sp
-        \\ bl  __divmodsi4
+        \\ bl  %[__divmodsi4]
         \\ ldr r1, [sp]
         \\ add sp, #4
         \\ pop {pc}
-        ::: "memory");
+        :
+        : [__divmodsi4] "X" (&__divmodsi4),
+        : "memory"
+    );
     unreachable;
 }
 
@@ -184,12 +193,15 @@ pub fn __aeabi_ldivmod() callconv(.Naked) void {
         \\ sub sp, #16
         \\ add r4, sp, #8
         \\ str r4, [sp]
-        \\ bl  __divmoddi4
+        \\ bl  %[__divmoddi4]
         \\ ldr r2, [sp, #8]
         \\ ldr r3, [sp, #12]
         \\ add sp, #16
         \\ pop {r4, pc}
-        ::: "memory");
+        :
+        : [__divmoddi4] "X" (&__divmoddi4),
+        : "memory"
+    );
     unreachable;
 }
 

lib/compiler_rt/aulldiv.zig

@@ -8,7 +8,7 @@ const common = @import("common.zig");
 pub const panic = common.panic;
 
 comptime {
-    if (arch == .x86 and os == .windows and (abi == .msvc or abi == .itanium) and builtin.zig_backend != .stage2_c) {
+    if (arch == .x86 and os == .windows and (abi == .msvc or abi == .itanium) and !builtin.link_libc) {
         // Don't let LLVM apply the stdcall name mangling on those MSVC builtins
         @export(&_alldiv, .{ .name = "\x01__alldiv", .linkage = common.linkage, .visibility = common.visibility });
         @export(&_aulldiv, .{ .name = "\x01__aulldiv", .linkage = common.linkage, .visibility = common.visibility });

lib/compiler_rt/aullrem.zig

@@ -8,7 +8,7 @@ const common = @import("common.zig");
 pub const panic = common.panic;
 
 comptime {
-    if (arch == .x86 and os == .windows and (abi == .msvc or abi == .itanium) and builtin.zig_backend != .stage2_c) {
+    if (arch == .x86 and os == .windows and (abi == .msvc or abi == .itanium) and !builtin.link_libc) {
         // Don't let LLVM apply the stdcall name mangling on those MSVC builtins
         @export(&_allrem, .{ .name = "\x01__allrem", .linkage = common.linkage, .visibility = common.visibility });
         @export(&_aullrem, .{ .name = "\x01__aullrem", .linkage = common.linkage, .visibility = common.visibility });

lib/compiler_rt/common.zig

@@ -9,11 +9,13 @@ else if (ofmt_c)
     .strong
 else
     .weak;
+
 /// Determines the symbol's visibility to other objects.
 /// For WebAssembly this allows the symbol to be resolved to other modules, but will not
 /// export it to the host runtime.
 pub const visibility: std.builtin.SymbolVisibility =
     if (builtin.target.isWasm() and linkage != .internal) .hidden else .default;
+
 pub const want_aeabi = switch (builtin.abi) {
     .eabi,
     .eabihf,
@@ -29,7 +31,9 @@ pub const want_aeabi = switch (builtin.abi) {
     },
     else => false,
 };
-pub const want_mingw_arm_abi = builtin.cpu.arch.isArm() and builtin.target.isMinGW();
+
+/// These functions are provided by libc when targeting MSVC, but not MinGW.
+pub const want_windows_arm_abi = builtin.cpu.arch.isArm() and builtin.os.tag == .windows and (builtin.abi.isGnu() or !builtin.link_libc);
 
 pub const want_ppc_abi = builtin.cpu.arch.isPowerPC();
 

lib/compiler_rt/fixdfdi.zig

@@ -8,11 +8,7 @@ comptime {
     if (common.want_aeabi) {
         @export(&__aeabi_d2lz, .{ .name = "__aeabi_d2lz", .linkage = common.linkage, .visibility = common.visibility });
     } else {
-        @export(&__fixdfdi, .{ .name = "__fixdfdi", .linkage = common.linkage, .visibility = common.visibility });
-
-        if (common.want_mingw_arm_abi) {
-            @export(&__fixdfdi, .{ .name = "__dtoi64", .linkage = common.linkage, .visibility = common.visibility });
-        }
+        @export(&__fixdfdi, .{ .name = if (common.want_windows_arm_abi) "__dtoi64" else "__fixdfdi", .linkage = common.linkage, .visibility = common.visibility });
     }
 }
 

lib/compiler_rt/fixsfdi.zig

@@ -8,11 +8,7 @@ comptime {
     if (common.want_aeabi) {
         @export(&__aeabi_f2lz, .{ .name = "__aeabi_f2lz", .linkage = common.linkage, .visibility = common.visibility });
     } else {
-        @export(&__fixsfdi, .{ .name = "__fixsfdi", .linkage = common.linkage, .visibility = common.visibility });
-
-        if (common.want_mingw_arm_abi) {
-            @export(&__fixsfdi, .{ .name = "__stoi64", .linkage = common.linkage, .visibility = common.visibility });
-        }
+        @export(&__fixsfdi, .{ .name = if (common.want_windows_arm_abi) "__stoi64" else "__fixsfdi", .linkage = common.linkage, .visibility = common.visibility });
     }
 }
 

lib/compiler_rt/fixunsdfdi.zig

@@ -8,11 +8,7 @@ comptime {
     if (common.want_aeabi) {
         @export(&__aeabi_d2ulz, .{ .name = "__aeabi_d2ulz", .linkage = common.linkage, .visibility = common.visibility });
     } else {
-        @export(&__fixunsdfdi, .{ .name = "__fixunsdfdi", .linkage = common.linkage, .visibility = common.visibility });
-
-        if (common.want_mingw_arm_abi) {
-            @export(&__fixunsdfdi, .{ .name = "__dtou64", .linkage = common.linkage, .visibility = common.visibility });
-        }
+        @export(&__fixunsdfdi, .{ .name = if (common.want_windows_arm_abi) "__dtou64" else "__fixunsdfdi", .linkage = common.linkage, .visibility = common.visibility });
     }
 }
 

lib/compiler_rt/fixunssfdi.zig

@@ -8,11 +8,7 @@ comptime {
     if (common.want_aeabi) {
         @export(&__aeabi_f2ulz, .{ .name = "__aeabi_f2ulz", .linkage = common.linkage, .visibility = common.visibility });
     } else {
-        @export(&__fixunssfdi, .{ .name = "__fixunssfdi", .linkage = common.linkage, .visibility = common.visibility });
-
-        if (common.want_mingw_arm_abi) {
-            @export(&__fixunssfdi, .{ .name = "__stou64", .linkage = common.linkage, .visibility = common.visibility });
-        }
+        @export(&__fixunssfdi, .{ .name = if (common.want_windows_arm_abi) "__stou64" else "__fixunssfdi", .linkage = common.linkage, .visibility = common.visibility });
     }
 }
 

lib/compiler_rt/floatdidf.zig

@@ -8,11 +8,7 @@ comptime {
     if (common.want_aeabi) {
         @export(&__aeabi_l2d, .{ .name = "__aeabi_l2d", .linkage = common.linkage, .visibility = common.visibility });
     } else {
-        @export(&__floatdidf, .{ .name = "__floatdidf", .linkage = common.linkage, .visibility = common.visibility });
-
-        if (common.want_mingw_arm_abi) {
-            @export(&__floatdidf, .{ .name = "__i64tod", .linkage = common.linkage, .visibility = common.visibility });
-        }
+        @export(&__floatdidf, .{ .name = if (common.want_windows_arm_abi) "__i64tod" else "__floatdidf", .linkage = common.linkage, .visibility = common.visibility });
     }
 }
 

lib/compiler_rt/floatdisf.zig

@@ -8,11 +8,7 @@ comptime {
     if (common.want_aeabi) {
         @export(&__aeabi_l2f, .{ .name = "__aeabi_l2f", .linkage = common.linkage, .visibility = common.visibility });
     } else {
-        @export(&__floatdisf, .{ .name = "__floatdisf", .linkage = common.linkage, .visibility = common.visibility });
-
-        if (common.want_mingw_arm_abi) {
-            @export(&__floatdisf, .{ .name = "__i64tos", .linkage = common.linkage, .visibility = common.visibility });
-        }
+        @export(&__floatdisf, .{ .name = if (common.want_windows_arm_abi) "__i64tos" else "__floatdisf", .linkage = common.linkage, .visibility = common.visibility });
     }
 }
 

lib/compiler_rt/floatundidf.zig

@@ -8,11 +8,7 @@ comptime {
     if (common.want_aeabi) {
         @export(&__aeabi_ul2d, .{ .name = "__aeabi_ul2d", .linkage = common.linkage, .visibility = common.visibility });
     } else {
-        @export(&__floatundidf, .{ .name = "__floatundidf", .linkage = common.linkage, .visibility = common.visibility });
-
-        if (common.want_mingw_arm_abi) {
-            @export(&__floatundidf, .{ .name = "__u64tod", .linkage = common.linkage, .visibility = common.visibility });
-        }
+        @export(&__floatundidf, .{ .name = if (common.want_windows_arm_abi) "__u64tod" else "__floatundidf", .linkage = common.linkage, .visibility = common.visibility });
     }
 }
 

lib/compiler_rt/floatundisf.zig

@@ -8,11 +8,7 @@ comptime {
     if (common.want_aeabi) {
         @export(&__aeabi_ul2f, .{ .name = "__aeabi_ul2f", .linkage = common.linkage, .visibility = common.visibility });
     } else {
-        @export(&__floatundisf, .{ .name = "__floatundisf", .linkage = common.linkage, .visibility = common.visibility });
-
-        if (common.want_mingw_arm_abi) {
-            @export(&__floatundisf, .{ .name = "__u64tos", .linkage = common.linkage, .visibility = common.visibility });
-        }
+        @export(&__floatundisf, .{ .name = if (common.want_windows_arm_abi) "__u64tos" else "__floatundisf", .linkage = common.linkage, .visibility = common.visibility });
     }
 }
 

src/Compilation.zig

@@ -1881,18 +1881,6 @@ pub fn create(gpa: Allocator, arena: Allocator, options: CreateOptions) !*Compil
                 comp.remaining_prelink_tasks += 1;
             }
 
-            if (target.isMinGW() and comp.config.any_non_single_threaded) {
-                // LLD might drop some symbols as unused during LTO and GCing, therefore,
-                // we force mark them for resolution here.
-
-                const tls_index_sym = switch (target.cpu.arch) {
-                    .x86 => "__tls_index",
-                    else => "_tls_index",
-                };
-
-                try comp.force_undefined_symbols.put(comp.gpa, tls_index_sym, {});
-            }
-
             if (comp.include_compiler_rt and capable_of_building_compiler_rt) {
                 if (is_exe_or_dyn_lib) {
                     log.debug("queuing a job to build compiler_rt_lib", .{});
@@ -3695,15 +3683,19 @@ fn performAllTheWorkInner(
     // In case it failed last time, try again. `clearMiscFailures` was already
     // called at the start of `update`.
     if (comp.queued_jobs.compiler_rt_lib and comp.compiler_rt_lib == null) {
-        comp.link_task_wait_group.spawnManager(buildRt, .{ comp, "compiler_rt.zig", .compiler_rt, .Lib, &comp.compiler_rt_lib, main_progress_node });
+        // LLVM disables LTO for its compiler-rt and we've had various issues with LTO of our
+        // compiler-rt due to LLD bugs as well, e.g.:
+        //
+        // https://github.com/llvm/llvm-project/issues/43698#issuecomment-2542660611
+        comp.link_task_wait_group.spawnManager(buildRt, .{ comp, "compiler_rt.zig", .compiler_rt, .Lib, false, &comp.compiler_rt_lib, main_progress_node });
     }
 
     if (comp.queued_jobs.compiler_rt_obj and comp.compiler_rt_obj == null) {
-        comp.link_task_wait_group.spawnManager(buildRt, .{ comp, "compiler_rt.zig", .compiler_rt, .Obj, &comp.compiler_rt_obj, main_progress_node });
+        comp.link_task_wait_group.spawnManager(buildRt, .{ comp, "compiler_rt.zig", .compiler_rt, .Obj, false, &comp.compiler_rt_obj, main_progress_node });
     }
 
     if (comp.queued_jobs.fuzzer_lib and comp.fuzzer_lib == null) {
-        comp.link_task_wait_group.spawnManager(buildRt, .{ comp, "fuzzer.zig", .libfuzzer, .Lib, &comp.fuzzer_lib, main_progress_node });
+        comp.link_task_wait_group.spawnManager(buildRt, .{ comp, "fuzzer.zig", .libfuzzer, .Lib, true, &comp.fuzzer_lib, main_progress_node });
     }
 
     if (comp.queued_jobs.glibc_shared_objects) {
@@ -4635,12 +4627,14 @@ fn buildRt(
     root_source_name: []const u8,
     misc_task: MiscTask,
     output_mode: std.builtin.OutputMode,
+    allow_lto: bool,
     out: *?CrtFile,
     prog_node: std.Progress.Node,
 ) void {
     comp.buildOutputFromZig(
         root_source_name,
         output_mode,
+        allow_lto,
         out,
         misc_task,
         prog_node,
@@ -4748,6 +4742,7 @@ fn buildZigLibc(comp: *Compilation, prog_node: std.Progress.Node) void {
     comp.buildOutputFromZig(
         "c.zig",
         .Lib,
+        true,
         &comp.libc_static_lib,
         .zig_libc,
         prog_node,
@@ -6453,6 +6448,7 @@ fn buildOutputFromZig(
     comp: *Compilation,
     src_basename: []const u8,
     output_mode: std.builtin.OutputMode,
+    allow_lto: bool,
     out: *?CrtFile,
     misc_task_tag: MiscTask,
     prog_node: std.Progress.Node,
@@ -6481,6 +6477,7 @@ fn buildOutputFromZig(
         .root_strip = strip,
         .link_libc = comp.config.link_libc,
         .any_unwind_tables = comp.root_mod.unwind_tables != .none,
+        .lto = if (allow_lto) comp.config.lto else .none,
     });
 
     const root_mod = try Package.Module.create(arena, .{
@@ -6581,6 +6578,8 @@ pub const CrtFileOptions = struct {
     unwind_tables: ?std.builtin.UnwindTables = null,
     pic: ?bool = null,
     no_builtin: ?bool = null,
+
+    allow_lto: bool = true,
 };
 
 pub fn build_crt_file(
@@ -6619,7 +6618,7 @@ pub fn build_crt_file(
         .link_libc = false,
         .any_unwind_tables = options.unwind_tables != .none,
         .lto = switch (output_mode) {
-            .Lib => comp.config.lto,
+            .Lib => if (options.allow_lto) comp.config.lto else .none,
             .Obj, .Exe => .none,
         },
     });

src/Compilation/Config.zig

@@ -295,27 +295,8 @@ pub fn resolve(options: Options) ResolveError!Config {
         }
 
         if (options.lto) |x| break :b x;
-        if (!options.any_c_source_files) break :b .none;
-
-        // https://github.com/llvm/llvm-project/pull/116537
-        switch (target.abi) {
-            .gnuabin32,
-            .gnuilp32,
-            .gnux32,
-            .ilp32,
-            .muslabin32,
-            .muslx32,
-            => break :b .none,
-            else => {},
-        }
 
-        break :b switch (options.output_mode) {
-            .Lib, .Obj => .none,
-            .Exe => switch (root_optimize_mode) {
-                .Debug => .none,
-                .ReleaseSafe, .ReleaseFast, .ReleaseSmall => .full,
-            },
-        };
+        break :b .none;
     };
 
     const link_libcpp = b: {

src/libtsan.zig

@@ -53,6 +53,8 @@ pub fn buildTsan(comp: *Compilation, prog_node: std.Progress.Node) BuildError!vo
     const optimize_mode = comp.compilerRtOptMode();
     const strip = comp.compilerRtStrip();
     const link_libcpp = target.isDarwin();
+    const unwind_tables: std.builtin.UnwindTables =
+        if (target.cpu.arch == .x86 and target.os.tag == .windows) .none else .@"async";
 
     const config = Compilation.Config.resolve(.{
         .output_mode = output_mode,
@@ -65,6 +67,9 @@ pub fn buildTsan(comp: *Compilation, prog_node: std.Progress.Node) BuildError!vo
         .root_strip = strip,
         .link_libc = true,
         .link_libcpp = link_libcpp,
+        .any_unwind_tables = unwind_tables != .none,
+        // LLVM disables LTO for its libtsan.
+        .lto = .none,
     }) catch |err| {
         comp.setMiscFailure(
             .libtsan,
@@ -95,6 +100,7 @@ pub fn buildTsan(comp: *Compilation, prog_node: std.Progress.Node) BuildError!vo
             .red_zone = comp.root_mod.red_zone,
             .omit_frame_pointer = optimize_mode != .Debug and !target.os.tag.isDarwin(),
             .valgrind = false,
+            .unwind_tables = unwind_tables,
             .optimize_mode = optimize_mode,
             .structured_cfg = comp.root_mod.structured_cfg,
             .pic = true,