Commit `0ff0bdb4a7`

wooster0 <wooster0@proton.me>

2024-12-19 15:42:59

Module: keep frame pointer in ReleaseSmall on x86

On x86 and x86_64 keeping the frame pointer usually reduces binary size, even for simple programs: ``` ~$ cat x.zig pub fn main() void { @import("std").debug.print("hello", .{}); } ~$ zig build-exe x.zig -target x86_64-linux -OReleaseSmall -fno-omit-frame-pointer && wc -c x 5168 x ~$ zig build-exe x.zig -target x86_64-linux -OReleaseSmall -fomit-frame-pointer && wc -c x 5216 x ``` ``` ~$ cat x.zig pub fn main() void { @import("std").debug.print("hello", .{}); } ~$ zig build-exe x.zig -target x86-linux -OReleaseSmall -fno-omit-frame-pointer && wc -c x 3400 x ~$ zig build-exe x.zig -target x86-linux -OReleaseSmall -fomit-frame-pointer && wc -c x 3556 x ``` A bigger benchmark is the Zig compiler: With no changes to anything on master branch: ``` $ zig build -Dno-lib -Dno-langref --zig-lib-dir lib -Doptimize=ReleaseSmall $ wc -c zig-out/bin/zig 10698792 zig-out/bin/zig ``` Adding `.omit_frame_pointer = false` in `addCompilerStep` in `build.zig`: ``` $ zig build -Dno-lib -Dno-langref --zig-lib-dir lib -Doptimize=ReleaseSmall $ wc -c zig-out/bin/zig 10155744 zig-out/bin/zig ```

master

1 parent e2e3633

Changed files (1)

src

Package

Module.zig

@@ -205,7 +205,12 @@ pub fn create(arena: Allocator, options: CreateOptions) !*Package.Module {
     const omit_frame_pointer = b: {
         if (options.inherited.omit_frame_pointer) |x| break :b x;
         if (options.parent) |p| break :b p.omit_frame_pointer;
-        if (optimize_mode == .ReleaseSmall) break :b true;
+        if (optimize_mode == .ReleaseSmall) {
+            // On x86, in most cases, keeping the frame pointer usually results in smaller binary size.
+            // This has to do with how instructions for memory access via the stack base pointer register (when keeping the frame pointer)
+            // are smaller than instructions for memory access via the stack pointer register (when omitting the frame pointer).
+            break :b !target.cpu.arch.isX86();
+        }
         break :b false;
     };

Commit 0ff0bdb4a7

Commit `0ff0bdb4a7`