add -Zoffload=Enable flag, to enable gpu (host) code generation

Author: ZuseZ4

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -120,6 +120,7 @@ pub struct ModuleConfig {
     pub emit_lifetime_markers: bool,
     pub llvm_plugins: Vec<String>,
     pub autodiff: Vec<config::AutoDiff>,
+    pub offload: Vec<config::Offload>,
 }
 
 impl ModuleConfig {
@@ -268,6 +269,7 @@ impl ModuleConfig {
             emit_lifetime_markers: sess.emit_lifetime_markers(),
             llvm_plugins: if_regular!(sess.opts.unstable_opts.llvm_plugins.clone(), vec![]),
             autodiff: if_regular!(sess.opts.unstable_opts.autodiff.clone(), vec![]),
+            offload: if_regular!(sess.opts.unstable_opts.offload.clone(), vec![]),
         }
     }
 

compiler/rustc_session/src/config.rs

@@ -226,6 +226,13 @@ pub enum CoverageLevel {
     Mcdc,
 }
 
+// The different settings that the `-Z offload` flag can have.
+#[derive(Clone, Copy, PartialEq, Hash, Debug)]
+pub enum Offload {
+    /// Enable the llvm offload pipeline
+    Enable,
+}
+
 /// The different settings that the `-Z autodiff` flag can have.
 #[derive(Clone, PartialEq, Hash, Debug)]
 pub enum AutoDiff {
@@ -3118,7 +3125,7 @@ pub(crate) mod dep_tracking {
         AutoDiff, BranchProtection, CFGuard, CFProtection, CollapseMacroDebuginfo, CoverageOptions,
         CrateType, DebugInfo, DebugInfoCompression, ErrorOutputType, FmtDebug, FunctionReturn,
         InliningThreshold, InstrumentCoverage, InstrumentXRay, LinkerPluginLto, LocationDetail,
-        LtoCli, MirStripDebugInfo, NextSolverConfig, OomStrategy, OptLevel, OutFileName,
+        LtoCli, MirStripDebugInfo, NextSolverConfig, Offload, OomStrategy, OptLevel, OutFileName,
         OutputType, OutputTypes, PatchableFunctionEntry, Polonius, RemapPathScopeComponents,
         ResolveDocLinks, SourceFileHashAlgorithm, SplitDwarfKind, SwitchWithOptPath,
         SymbolManglingVersion, WasiExecModel,
@@ -3165,6 +3172,7 @@ pub(crate) mod dep_tracking {
     impl_dep_tracking_hash_via_hash!(
         (),
         AutoDiff,
+        Offload,
         bool,
         usize,
         NonZero<usize>,

compiler/rustc_session/src/options.rs

@@ -726,6 +726,7 @@ mod desc {
     pub(crate) const parse_list_with_polarity: &str =
         "a comma-separated list of strings, with elements beginning with + or -";
     pub(crate) const parse_autodiff: &str = "a comma separated list of settings: `Enable`, `PrintSteps`, `PrintTA`, `PrintTAFn`, `PrintAA`, `PrintPerf`, `PrintModBefore`, `PrintModAfter`, `PrintModFinal`, `PrintPasses`, `NoPostopt`, `LooseTypes`, `Inline`";
+    pub(crate) const parse_offload: &str = "a comma separated list of settings: `Enable`";
     pub(crate) const parse_comma_list: &str = "a comma-separated list of strings";
     pub(crate) const parse_opt_comma_list: &str = parse_comma_list;
     pub(crate) const parse_number: &str = "a number";
@@ -1357,6 +1358,27 @@ pub mod parse {
         }
     }
 
+    pub(crate) fn parse_offload(slot: &mut Vec<Offload>, v: Option<&str>) -> bool {
+        let Some(v) = v else {
+            *slot = vec![];
+            return true;
+        };
+        let mut v: Vec<&str> = v.split(",").collect();
+        v.sort_unstable();
+        for &val in v.iter() {
+            let variant = match val {
+                "Enable" => Offload::Enable,
+                _ => {
+                    // FIXME(ZuseZ4): print an error saying which value is not recognized
+                    return false;
+                }
+            };
+            slot.push(variant);
+        }
+
+        true
+    }
+
     pub(crate) fn parse_autodiff(slot: &mut Vec<AutoDiff>, v: Option<&str>) -> bool {
         let Some(v) = v else {
             *slot = vec![];
@@ -2399,6 +2421,11 @@ options! {
         "do not use unique names for text and data sections when -Z function-sections is used"),
     normalize_docs: bool = (false, parse_bool, [TRACKED],
         "normalize associated items in rustdoc when generating documentation"),
+    offload: Vec<crate::config::Offload> = (Vec::new(), parse_offload, [TRACKED],
+        "a list of offload flags to enable
+        Mandatory setting:
+        `=Enable`
+        Currently the only option available"),
     on_broken_pipe: OnBrokenPipe = (OnBrokenPipe::Default, parse_on_broken_pipe, [TRACKED],
         "behavior of std::io::ErrorKind::BrokenPipe (SIGPIPE)"),
     oom: OomStrategy = (OomStrategy::Abort, parse_oom_strategy, [TRACKED],