Add -Z llvm_module_flag

Allow adding values to the `!llvm.module.flags` metadata for a generated
module.  The syntax is

`-Z llvm_module_flag=<name>:<type>:<value>:<behavior>`

Currently only u32 values are supported but the type is required to be
specified for forward compatibility.  The `behavior` element must match
one of the named LLVM metadata behaviors.viors.

This flag is expected to be perma-unstable.

1 files changed, 30 insertions, 0 deletions

diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 76d69646f1d..2840c783aa8 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -429,6 +429,7 @@ mod desc {
     pub const parse_remap_path_scope: &str = "comma separated list of scopes: `macro`, `diagnostics`, `unsplit-debuginfo`, `split-debuginfo`, `split-debuginfo-path`, `object`, `all`";
     pub const parse_inlining_threshold: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), or a non-negative number";
+    pub const parse_llvm_module_flag: &str = "<key>:<type>:<value>:<behavior>. Type must currently be `u32`. Behavior should be one of (`error`, `warning`, `require`, `override`, `append`, `appendunique`, `max`, `min`)";
 }
 
 mod parse {
@@ -1331,6 +1332,33 @@ mod parse {
         }
         true
     }
+
+    pub(crate) fn parse_llvm_module_flag(
+        slot: &mut Vec<(String, u32, String)>,
+        v: Option<&str>,
+    ) -> bool {
+        let elements = v.unwrap_or_default().split(':').collect::<Vec<_>>();
+        let [key, md_type, value, behavior] = elements.as_slice() else {
+            return false;
+        };
+        if *md_type != "u32" {
+            // Currently we only support u32 metadata flags, but require the
+            // type for forward-compatibility.
+            return false;
+        }
+        let Ok(value) = value.parse::<u32>() else {
+            return false;
+        };
+        let behavior = behavior.to_lowercase();
+        let all_behaviors =
+            ["error", "warning", "require", "override", "append", "appendunique", "max", "min"];
+        if !all_behaviors.contains(&behavior.as_str()) {
+            return false;
+        }
+
+        slot.push((key.to_string(), value, behavior));
+        true
+    }
 }
 
 options! {
@@ -1631,6 +1659,8 @@ options! {
         "link native libraries in the linker invocation (default: yes)"),
     link_only: bool = (false, parse_bool, [TRACKED],
         "link the `.rlink` file generated by `-Z no-link` (default: no)"),
+    llvm_module_flag: Vec<(String, u32, String)> = (Vec::new(), parse_llvm_module_flag, [TRACKED],
+        "a list of module flags to pass to LLVM (space separated)"),
     llvm_plugins: Vec<String> = (Vec::new(), parse_list, [TRACKED],
         "a list LLVM plugins to enable (space separated)"),
     llvm_time_trace: bool = (false, parse_bool, [UNTRACKED],