std.Target: Define and use lime1 as the baseline CPU model for WebAssembly.

See: WebAssembly/tool-conventions#235

This is not *quite* using the same features as the spec'd lime1 model because
LLVM 19 doesn't have the level of feature granularity that we need for that.
This will be fixed once we upgrade to LLVM 20.

Part of ziglang#21818.

Author: alexrp

build.zig

@@ -592,7 +592,10 @@ fn addWasiUpdateStep(b: *std.Build, version: [:0]const u8) !void {
         .cpu_arch = .wasm32,
         .os_tag = .wasi,
     };
-    target_query.cpu_features_add.addFeature(@intFromEnum(std.Target.wasm.Feature.bulk_memory));
+    // Not supported by the `wasm-opt` version in CI.
+    target_query.cpu_features_add.removeFeature(@intFromEnum(std.Target.wasm.Feature.extended_const));
+    // Not supported by `wasm2c`.
+    target_query.cpu_features_add.removeFeature(@intFromEnum(std.Target.wasm.Feature.nontrapping_fptoint));
 
     const exe = addCompilerStep(b, .{
         .optimize = .ReleaseSmall,
@@ -620,6 +623,7 @@ fn addWasiUpdateStep(b: *std.Build, version: [:0]const u8) !void {
         "wasm-opt",
         "-Oz",
         "--enable-bulk-memory",
+        "--enable-mutable-globals",
         "--enable-sign-ext",
     });
     run_opt.addArtifactArg(exe);

lib/std/Target.zig

@@ -2006,7 +2006,7 @@ pub const Cpu = struct {
                     else => generic(arch),
                 },
                 .xcore => &xcore.cpu.xs1b_generic,
-                .wasm32, .wasm64 => &wasm.cpu.generic,
+                .wasm32, .wasm64 => &wasm.cpu.lime1,
 
                 else => generic(arch),
             };

lib/std/Target/wasm.zig

@@ -139,6 +139,18 @@ pub const cpu = struct {
             .sign_ext,
         }),
     };
+    pub const lime1: CpuModel = .{
+        .name = "lime1",
+        .llvm_name = null,
+        .features = featureSet(&[_]Feature{
+            .bulk_memory,
+            .extended_const,
+            .multivalue,
+            .mutable_globals,
+            .nontrapping_fptoint,
+            .sign_ext,
+        }),
+    };
     pub const mvp: CpuModel = .{
         .name = "mvp",
         .llvm_name = "mvp",

src/Compilation.zig

@@ -4004,14 +4004,9 @@ fn workerDocsWasmFallible(comp: *Compilation, prog_node: std.Progress.Node) anye
             .os_tag = .freestanding,
             .cpu_features_add = std.Target.wasm.featureSet(&.{
                 .atomics,
-                .bulk_memory,
                 // .extended_const, not supported by Safari
-                .multivalue,
-                .mutable_globals,
-                .nontrapping_fptoint,
                 .reference_types,
                 //.relaxed_simd, not supported by Firefox or Safari
-                .sign_ext,
                 // observed to cause Error occured during wast conversion :
                 // Unknown operator: 0xfd058 in Firefox 117
                 //.simd128,

tools/update_cpu_features.zig

@@ -1033,6 +1033,20 @@ const llvm_targets = [_]LlvmTarget{
         .zig_name = "wasm",
         .llvm_name = "WebAssembly",
         .td_name = "WebAssembly.td",
+        .extra_cpus = &.{
+            .{
+                .llvm_name = null,
+                .zig_name = "lime1",
+                .features = &.{
+                    "bulk_memory",
+                    "extended_const",
+                    "multivalue",
+                    "mutable_globals",
+                    "nontrapping_fptoint",
+                    "sign_ext",
+                },
+            },
+        },
     },
     .{
         .zig_name = "x86",