Enable DataflowConstProp by default.

Author: cjgillot

compiler/rustc_mir_transform/src/dataflow_const_prop.rs

@@ -23,23 +23,18 @@ use crate::const_prop::throw_machine_stop_str;
 
 // These constants are somewhat random guesses and have not been optimized.
 // If `tcx.sess.mir_opt_level() >= 4`, we ignore the limits (this can become very expensive).
-const BLOCK_LIMIT: usize = 100;
 const PLACE_LIMIT: usize = 100;
 
 pub struct DataflowConstProp;
 
 impl<'tcx> MirPass<'tcx> for DataflowConstProp {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() >= 3
+        sess.mir_opt_level() >= 2
     }
 
     #[instrument(skip_all level = "debug")]
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         debug!(def_id = ?body.source.def_id());
-        if tcx.sess.mir_opt_level() < 4 && body.basic_blocks.len() > BLOCK_LIMIT {
-            debug!("aborted dataflow const prop due too many basic blocks");
-            return;
-        }
 
         // We want to have a somewhat linear runtime w.r.t. the number of statements/terminators.
         // Let's call this number `n`. Dataflow analysis has `O(h*n)` transfer function

tests/coverage/closure.cov-map

@@ -33,20 +33,16 @@ Number of file 0 mappings: 24
 - Code(Expression(1, Add)) at (prev + 1, 5) to (start + 3, 2)
     = (c1 + (c0 - c1))
 
-Function name: closure::main::{closure#0}
-Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 27, 05, 02, 14, 05, 02, 15, 02, 0a, 02, 02, 0a, 00, 0b, 07, 01, 09, 01, 06]
+Function name: closure::main::{closure#0} (unused)
+Raw bytes (24): 0x[01, 01, 00, 04, 00, 27, 05, 02, 14, 00, 02, 15, 02, 0a, 00, 02, 0a, 00, 0b, 00, 01, 09, 01, 06]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
-- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(1), rhs = Expression(0, Sub)
+Number of expressions: 0
 Number of file 0 mappings: 4
-- Code(Counter(0)) at (prev + 39, 5) to (start + 2, 20)
-- Code(Counter(1)) at (prev + 2, 21) to (start + 2, 10)
-- Code(Expression(0, Sub)) at (prev + 2, 10) to (start + 0, 11)
-    = (c0 - c1)
-- Code(Expression(1, Add)) at (prev + 1, 9) to (start + 1, 6)
-    = (c1 + (c0 - c1))
+- Code(Zero) at (prev + 39, 5) to (start + 2, 20)
+- Code(Zero) at (prev + 2, 21) to (start + 2, 10)
+- Code(Zero) at (prev + 2, 10) to (start + 0, 11)
+- Code(Zero) at (prev + 1, 9) to (start + 1, 6)
 
 Function name: closure::main::{closure#10} (unused)
 Raw bytes (10): 0x[01, 01, 00, 01, 00, 9a, 01, 07, 00, 21]
@@ -148,20 +144,16 @@ Number of file 0 mappings: 6
 - Code(Expression(0, Add)) at (prev + 2, 9) to (start + 0, 10)
     = (c1 + (c0 - c1))
 
-Function name: closure::main::{closure#18}
-Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 18, 0d, 02, 1c, 05, 02, 1d, 02, 12, 02, 02, 12, 00, 13, 07, 01, 11, 01, 0e]
+Function name: closure::main::{closure#18} (unused)
+Raw bytes (24): 0x[01, 01, 00, 04, 00, 18, 0d, 02, 1c, 00, 02, 1d, 02, 12, 00, 02, 12, 00, 13, 00, 01, 11, 01, 0e]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
-- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(1), rhs = Expression(0, Sub)
+Number of expressions: 0
 Number of file 0 mappings: 4
-- Code(Counter(0)) at (prev + 24, 13) to (start + 2, 28)
-- Code(Counter(1)) at (prev + 2, 29) to (start + 2, 18)
-- Code(Expression(0, Sub)) at (prev + 2, 18) to (start + 0, 19)
-    = (c0 - c1)
-- Code(Expression(1, Add)) at (prev + 1, 17) to (start + 1, 14)
-    = (c1 + (c0 - c1))
+- Code(Zero) at (prev + 24, 13) to (start + 2, 28)
+- Code(Zero) at (prev + 2, 29) to (start + 2, 18)
+- Code(Zero) at (prev + 2, 18) to (start + 0, 19)
+- Code(Zero) at (prev + 1, 17) to (start + 1, 14)
 
 Function name: closure::main::{closure#19}
 Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 42, 0d, 02, 1c, 05, 02, 1d, 02, 12, 02, 02, 12, 00, 13, 07, 01, 11, 01, 0e]