Add FixedUnitCount codegen unit partitioning strategy.

Author: michaelwoerister

src/librustc_trans/base.rs

@@ -58,7 +58,7 @@ use attributes;
 use build::*;
 use builder::{Builder, noname};
 use callee::{Callee, CallArgs, ArgExprs, ArgVals};
-use partitioning;
+use partitioning::{self, PartitioningStrategy};
 use cleanup::{self, CleanupMethods, DropHint};
 use closure;
 use common::{Block, C_bool, C_bytes_in_context, C_i32, C_int, C_uint, C_integral};
@@ -2938,8 +2938,17 @@ fn collect_translation_items<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>) {
         collector::collect_crate_translation_items(&ccx, collection_mode)
     });
 
+    let strategy = if ccx.sess().opts.debugging_opts.incremental.is_some() {
+        PartitioningStrategy::PerModule
+    } else {
+        PartitioningStrategy::FixedUnitCount(ccx.sess().opts.cg.codegen_units)
+    };
+
     let codegen_units = time(time_passes, "codegen unit partitioning", || {
-        partitioning::partition(ccx.tcx(), items.iter().cloned(), &inlining_map)
+        partitioning::partition(ccx.tcx(),
+                                items.iter().cloned(),
+                                strategy,
+                                &inlining_map)
     });
 
     if ccx.sess().opts.debugging_opts.print_trans_items.is_some() {

src/librustc_trans/partitioning.rs

@@ -132,19 +132,29 @@ pub struct CodegenUnit<'tcx> {
     pub items: FnvHashMap<TransItem<'tcx>, llvm::Linkage>,
 }
 
+pub enum PartitioningStrategy {
+    PerModule,
+    FixedUnitCount(usize)
+}
+
 // Anything we can't find a proper codegen unit for goes into this.
 const FALLBACK_CODEGEN_UNIT: &'static str = "__rustc_fallback_codegen_unit";
 
 pub fn partition<'tcx, I>(tcx: &TyCtxt<'tcx>,
                           trans_items: I,
+                          strategy: PartitioningStrategy,
                           inlining_map: &InliningMap<'tcx>)
                           -> Vec<CodegenUnit<'tcx>>
     where I: Iterator<Item = TransItem<'tcx>>
 {
     // In the first step, we place all regular translation items into their
     // respective 'home' codegen unit. Regular translation items are all
     // functions and statics defined in the local crate.
-    let initial_partitioning = place_root_translation_items(tcx, trans_items);
+    let mut initial_partitioning = place_root_translation_items(tcx, trans_items);
+
+    if let PartitioningStrategy::FixedUnitCount(count) = strategy {
+        merge_codegen_units(&mut initial_partitioning, count, &tcx.crate_name[..]);
+    }
 
     // In the next step, we use the inlining map to determine which addtional
     // translation items have to go into each codegen unit. These additional
@@ -217,6 +227,33 @@ fn place_root_translation_items<'tcx, I>(tcx: &TyCtxt<'tcx>,
     }
 }
 
+fn merge_codegen_units<'tcx>(initial_partitioning: &mut InitialPartitioning<'tcx>,
+                             target_cgu_count: usize,
+                             crate_name: &str) {
+    if target_cgu_count >= initial_partitioning.codegen_units.len() {
+        return;
+    }
+
+    assert!(target_cgu_count >= 1);
+    let codegen_units = &mut initial_partitioning.codegen_units;
+
+    // Merge the two smallest codegen units until the target size is reached
+    while codegen_units.len() > target_cgu_count {
+        // Sort small cgus to the back
+        codegen_units.as_mut_slice().sort_by_key(|cgu| -(cgu.items.len() as i64));
+        let smallest = codegen_units.pop().unwrap();
+        let second_smallest = codegen_units.last_mut().unwrap();
+
+        for (k, v) in smallest.items.into_iter() {
+            second_smallest.items.insert(k, v);
+        }
+    }
+
+    for (index, cgu) in codegen_units.iter_mut().enumerate() {
+        cgu.name = token::intern_and_get_ident(&format!("{}.{}", crate_name, index)[..]);
+    }
+}
+
 fn place_inlined_translation_items<'tcx>(initial_partitioning: InitialPartitioning<'tcx>,
                                          inlining_map: &InliningMap<'tcx>)
                                          -> Vec<CodegenUnit<'tcx>> {

src/test/codegen-units/partitioning/extern-drop-glue.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags:-Zprint-trans-items=lazy
+// compile-flags:-Zprint-trans-items=lazy -Zincremental=""
 
 #![allow(dead_code)]
 #![crate_type="lib"]

src/test/codegen-units/partitioning/extern-generic.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags:-Zprint-trans-items=eager
+// compile-flags:-Zprint-trans-items=eager -Zincremental=""
 
 #![allow(dead_code)]
 #![crate_type="lib"]

src/test/codegen-units/partitioning/inlining-from-extern-crate.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags:-Zprint-trans-items=lazy
+// compile-flags:-Zprint-trans-items=lazy -Zincremental=""
 
 #![crate_type="lib"]
 

src/test/codegen-units/partitioning/local-drop-glue.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags:-Zprint-trans-items=lazy
+// compile-flags:-Zprint-trans-items=lazy -Zincremental=""
 
 #![allow(dead_code)]
 #![crate_type="lib"]

src/test/codegen-units/partitioning/local-generic.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags:-Zprint-trans-items=eager
+// compile-flags:-Zprint-trans-items=eager -Zincremental=""
 
 #![allow(dead_code)]
 #![crate_type="lib"]

src/test/codegen-units/partitioning/local-inlining.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags:-Zprint-trans-items=lazy
+// compile-flags:-Zprint-trans-items=lazy -Zincremental=""
 
 #![allow(dead_code)]
 #![crate_type="lib"]

src/test/codegen-units/partitioning/local-transitive-inlining.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags:-Zprint-trans-items=lazy
+// compile-flags:-Zprint-trans-items=lazy -Zincremental=""
 
 #![allow(dead_code)]
 #![crate_type="lib"]

src/test/codegen-units/partitioning/methods-are-with-self-type.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags:-Zprint-trans-items=lazy
+// compile-flags:-Zprint-trans-items=lazy -Zincremental=""
 
 #![allow(dead_code)]