Subject: [bug#67075] [PATCH] build: zig-build-system: Add CPU option

From: Ekaitz Zarraga <[email-masked]>
Date: Sat, 18 Nov 2023 17:52:48 +0100

Hi,

Following Efraim's suggestion I arranged a new patch around the tuning 
option. I needed to patch Zig itself to use baseline cpu by default, 
which is safer in general for us.

If anyone need a more specific cpu, can use the tuning option to choose it.

Maybe I should split the changes in Zig and the tuning system, but if I 
do they wont appear together, and they mostly only make sense if applied 
at once.

Please let me know if you like this one better.

Hope it's cool.

Cheers,
Ekaitz

From 03616b9764278e05d74f8e8bf5d65b043603a437 Mon Sep 17 00:00:00 2001
Message-ID: <[email-masked]>
From: Ekaitz Zarraga <[email-masked]>
Date: Sat, 18 Nov 2023 17:29:07 +0100
Subject: [PATCH] gnu: zig: Make compiler tunable.

In order to make Zig tunable, we have to make sure by default it does
the right thing, that is use the `baseline` CPU instead of the `native`
one because the tuning system only adds an extra flag to the compiler
command line execution.

* gnu/packages/patches/zig-use-baseline-cpu-by-default.patch: Add file.
* gnu/packages/zig.scm(zig-0.10.1): Apply patch above.
* guix/transformations.scm(tuning-compiler): Add support for zig.

Change-Id: I40bd28071c97c0dd0a907c704072b52b26d2de28
---
 .../zig-use-baseline-cpu-by-default.patch     | 36 +++++++++++++++++++
 gnu/packages/zig.scm                          |  3 +-
 guix/transformations.scm                      | 22 ++++++++----
 3 files changed, 54 insertions(+), 7 deletions(-)
 create mode 100644 gnu/packages/patches/zig-use-baseline-cpu-by-default.patch

diff --git a/gnu/packages/patches/zig-use-baseline-cpu-by-default.patch b/gnu/packages/patches/zig-use-baseline-cpu-by-default.patch
new file mode 100644
index 0000000000..be78d9c6c7
--- /dev/null
+++ b/gnu/packages/patches/zig-use-baseline-cpu-by-default.patch
@@ -0,0 +1,36 @@
+From 1dc188129950031243c5a0c80ec2562fab8ec549 Mon Sep 17 00:00:00 2001
+From: Ekaitz Zarraga <[email-masked]>
+Date: Sat, 18 Nov 2023 15:04:16 +0100
+Subject: [PATCH] Use `baseline` cpu by default.
+
+This helps Guix tune the package later. Tunning will only add
+`-Dcpu=whatever` which should override the standard behaviour.
+
+Zig by default uses `native`, which interferes with our build process.
+In our previous zig-build-system we chose to add `-Dcpu=baseline` flag
+in each `zig build` execution, but that doesn't allow us to tune the
+package later. Tunning is only designed to add extra flags in the
+command line call, and we already had one set for the baseline case.
+With this patch we set the standard behavior to `baseline` so we don't
+need to add the `-Dcpu=baseline` flag in the zig-build-system and we can
+tune with no issues.
+---
+ lib/std/zig/CrossTarget.zig | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/lib/std/zig/CrossTarget.zig b/lib/std/zig/CrossTarget.zig
+index 6c59a4a3a..f5ec065fe 100644
+--- a/lib/std/zig/CrossTarget.zig
++++ b/lib/std/zig/CrossTarget.zig
+@@ -12,7 +12,7 @@ const mem = std.mem;
+ /// `null` means native.
+ cpu_arch: ?Target.Cpu.Arch = null,
+ 
+-cpu_model: CpuModel = CpuModel.determined_by_cpu_arch,
++cpu_model: CpuModel = CpuModel.baseline,
+ 
+ /// Sparse set of CPU features to add to the set from `cpu_model`.
+ cpu_features_add: Target.Cpu.Feature.Set = Target.Cpu.Feature.Set.empty,
+-- 
+2.41.0
+
diff --git a/gnu/packages/zig.scm b/gnu/packages/zig.scm
index dcca9a1121..82b83f44c2 100644
--- a/gnu/packages/zig.scm
+++ b/gnu/packages/zig.scm
@@ -42,7 +42,8 @@ (define-public zig-0.10
        (file-name (git-file-name name version))
        (sha256
         (base32 "1sh5xjsksl52i4cfv1qj36sz5h0ln7cq4pdhgs3960mk8a90im7b"))
-       (patches (search-patches "zig-do-not-link-against-librt.patch"))))
+       (patches (search-patches "zig-do-not-link-against-librt.patch"
+                                "zig-use-Dcpu-baseline-by-default.patch"))))
     (build-system cmake-build-system)
     (inputs
      (list clang-15 ; Clang propagates llvm.
diff --git a/guix/transformations.scm b/guix/transformations.scm
index 9cba6bedab..8964feb046 100644
--- a/guix/transformations.scm
+++ b/guix/transformations.scm
@@ -439,7 +439,8 @@ (define tuning-compiler
 actual compiler."
     (define wrapper
       #~(begin
-          (use-modules (ice-9 match))
+          (use-modules (ice-9 match)
+                       (ice-9 string-fun))
 
           (define psabi #$(gcc-architecture->micro-architecture-level
                             micro-architecture))
@@ -486,11 +487,20 @@ (define tuning-compiler
                 (apply
                   execl next
                        (append (cons next arguments)
-                         (if (and (search-next "go")
+                         (cond
+                           ((and (search-next "go")
                                   (string=? next (search-next "go")))
-                           '()
-                           (list (string-append "-march="
-                                                #$micro-architecture)))))))))))
+                           '())
+                           ((and (search-next "zig")
+                                  (string=? next (search-next "zig"))
+                            (list (string-append
+                                    ;; https://issues.guix.gnu.org/67075#3
+                                    "-Dcpu="
+                                    (string-replace-substring
+                                      #$micro-architecture "-" "_")))))
+                           (else
+                             (list (string-append "-march="
+                                     #$micro-architecture))))))))))))
 
     (define program
       (program-file (string-append "tuning-compiler-wrapper-" micro-architecture)
@@ -508,7 +518,7 @@ (define tuning-compiler
                                      (symlink #$program
                                               (string-append bin "/" program)))
                                    '("cc" "gcc" "clang" "g++" "c++" "clang++"
-                                     "go")))))))
+                                     "go" "zig")))))))
 
 (define (build-system-with-tuning-compiler bs micro-architecture)
   "Return a variant of BS, a build system, that ensures that the compiler that

base-commit: a514973413dc8179100ef8f0fcf41f5ac38c982f
-- 
2.41.0