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

From 03616b9764278e05d74f8e8bf5d65b043603a437 Mon Sep 17 00:00:00 2001
Message-ID: <03616b9764278e05d74f8e8bf5d65b043603a437.1700325640.git.ekaitz@elenq.tech>
From: Ekaitz Zarraga <ekaitz@elenq.tech>
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 <ekaitz@elenq.tech>
+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