Reverts #117206

cc @cjgillot @tmiasko

This revert is based on the following report of a regression caused by this PR:

#121094

In accordance with the compiler team [revert policy], PRs that cause meaningful
regressions should be reverted and re-landed once the regression has been fixed
(and a regression test has been added, where appropriate).
[revert policy]: https://forge.rust-lang.org/compiler/reviews.html#reverts

Fear not! Regressions happen. Please rest assured that this does not
represent a negative judgment of your contribution or ability to contribute
positively to Rust in the future. We simply want to prioritize keeping existing
use cases working, and keep the compiler more stable for everyone.

r? compiler

Author: erickt

compiler/rustc_mir_transform/src/jump_threading.rs

@@ -60,7 +60,7 @@ const MAX_PLACES: usize = 100;
 
 impl<'tcx> MirPass<'tcx> for JumpThreading {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() >= 2
+        sess.mir_opt_level() >= 4
     }
 
     #[instrument(skip_all level = "debug")]

tests/coverage/closure.cov-map

@@ -33,16 +33,20 @@ 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} (unused)
-Raw bytes (24): 0x[01, 01, 00, 04, 00, 28, 05, 02, 14, 00, 02, 15, 02, 0a, 00, 02, 0a, 00, 0b, 00, 01, 09, 01, 06]
+Function name: closure::main::{closure#0}
+Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 28, 05, 02, 14, 05, 02, 15, 02, 0a, 02, 02, 0a, 00, 0b, 07, 01, 09, 01, 06]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 0
+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 file 0 mappings: 4
-- Code(Zero) at (prev + 40, 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)
+- Code(Counter(0)) at (prev + 40, 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))
 
 Function name: closure::main::{closure#10} (unused)
 Raw bytes (10): 0x[01, 01, 00, 01, 00, 9b, 01, 07, 00, 21]
@@ -144,16 +148,20 @@ 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} (unused)
-Raw bytes (24): 0x[01, 01, 00, 04, 00, 19, 0d, 02, 1c, 00, 02, 1d, 02, 12, 00, 02, 12, 00, 13, 00, 01, 11, 01, 0e]
+Function name: closure::main::{closure#18}
+Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 19, 0d, 02, 1c, 05, 02, 1d, 02, 12, 02, 02, 12, 00, 13, 07, 01, 11, 01, 0e]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 0
+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 file 0 mappings: 4
-- Code(Zero) at (prev + 25, 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)
+- Code(Counter(0)) at (prev + 25, 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))
 
 Function name: closure::main::{closure#19}
 Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 43, 0d, 02, 1c, 05, 02, 1d, 02, 12, 02, 02, 12, 00, 13, 07, 01, 11, 01, 0e]

tests/coverage/issue-84561.cov-map

@@ -77,7 +77,7 @@ Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 167, 9) to (start + 2, 10)
 
 Function name: issue_84561::test3
-Raw bytes (436): 0x[01, 01, 41, 05, 09, 0d, 00, 15, 19, 12, 00, 15, 19, 21, 00, 1e, 00, 21, 00, 31, 00, 3d, 41, 2e, 45, 3d, 41, 42, 49, 45, 00, 3f, 51, 42, 49, 45, 00, 5d, 8a, 01, 8f, 01, 5d, 92, 01, 55, 51, 00, 92, 01, 55, 51, 00, 8f, 01, 5d, 92, 01, 55, 51, 00, 87, 01, 61, 5d, 8a, 01, 8f, 01, 5d, 92, 01, 55, 51, 00, 82, 01, 65, 87, 01, 61, 5d, 8a, 01, 8f, 01, 5d, 92, 01, 55, 51, 00, 75, f6, 01, fb, 01, 79, 00, fe, 01, 82, 02, 00, 69, 6d, 00, fe, 01, 82, 02, 00, 69, 6d, 69, 6d, 82, 02, 00, 69, 6d, fb, 01, 79, 00, fe, 01, 82, 02, 00, 69, 6d, f3, 01, 7d, 75, f6, 01, fb, 01, 79, 00, fe, 01, 82, 02, 00, 69, 6d, ee, 01, 00, f3, 01, 7d, 75, f6, 01, fb, 01, 79, 00, fe, 01, 82, 02, 00, 69, 6d, 33, 01, 08, 01, 03, 1c, 05, 04, 09, 01, 1c, 02, 02, 05, 04, 1f, 0d, 05, 05, 00, 1f, 06, 01, 05, 00, 1f, 15, 01, 09, 01, 1c, 12, 02, 05, 00, 1f, 0e, 01, 05, 00, 0f, 00, 00, 20, 00, 30, 21, 01, 05, 03, 0f, 00, 03, 20, 00, 30, 00, 00, 33, 00, 41, 00, 00, 4b, 00, 5a, 1e, 01, 05, 00, 0f, 00, 05, 09, 03, 10, 00, 05, 0d, 00, 1b, 00, 02, 0d, 00, 1c, 1a, 04, 09, 05, 06, 31, 06, 05, 03, 06, 22, 04, 05, 03, 06, 3d, 04, 09, 04, 06, 2e, 05, 08, 00, 0f, 45, 01, 09, 03, 0a, 2a, 05, 09, 03, 0a, 3f, 05, 08, 00, 0f, 51, 01, 09, 00, 13, 00, 03, 0d, 00, 1d, 3a, 03, 09, 00, 13, 00, 03, 0d, 00, 1d, 87, 01, 03, 05, 00, 0f, 8f, 01, 01, 0c, 00, 13, 5d, 01, 0d, 00, 13, 8a, 01, 02, 0d, 00, 13, 82, 01, 04, 05, 02, 13, 65, 03, 0d, 00, 13, 7e, 02, 0d, 00, 13, f3, 01, 03, 05, 00, 0f, 69, 01, 0c, 00, 13, 6d, 01, 0d, 03, 0e, 75, 04, 0d, 00, 13, fb, 01, 02, 0d, 00, 17, 82, 02, 01, 14, 00, 1b, 00, 01, 15, 00, 1b, fe, 01, 02, 15, 00, 1b, f6, 01, 04, 0d, 00, 13, 7d, 03, 09, 00, 19, ee, 01, 02, 05, 00, 0f, ea, 01, 03, 09, 00, 22, 00, 02, 05, 00, 0f, 00, 03, 09, 00, 2c, 00, 02, 01, 00, 02]
+Raw bytes (436): 0x[01, 01, 41, 05, 09, 0d, 00, 15, 19, 12, 00, 15, 19, 21, 00, 1e, 00, 21, 00, 31, 00, 3d, 41, 2e, 45, 3d, 41, 42, 49, 45, 00, 3f, 51, 42, 49, 45, 00, 5d, 8a, 01, 8f, 01, 5d, 92, 01, 55, 51, 00, 92, 01, 55, 51, 00, 8f, 01, 5d, 92, 01, 55, 51, 00, 87, 01, 61, 5d, 8a, 01, 8f, 01, 5d, 92, 01, 55, 51, 00, 82, 01, 65, 87, 01, 61, 5d, 8a, 01, 8f, 01, 5d, 92, 01, 55, 51, 00, 75, f6, 01, fb, 01, 79, 71, fe, 01, 82, 02, 71, 69, 6d, 71, fe, 01, 82, 02, 71, 69, 6d, 69, 6d, 82, 02, 71, 69, 6d, fb, 01, 79, 71, fe, 01, 82, 02, 71, 69, 6d, f3, 01, 7d, 75, f6, 01, fb, 01, 79, 71, fe, 01, 82, 02, 71, 69, 6d, ee, 01, 00, f3, 01, 7d, 75, f6, 01, fb, 01, 79, 71, fe, 01, 82, 02, 71, 69, 6d, 33, 01, 08, 01, 03, 1c, 05, 04, 09, 01, 1c, 02, 02, 05, 04, 1f, 0d, 05, 05, 00, 1f, 06, 01, 05, 00, 1f, 15, 01, 09, 01, 1c, 12, 02, 05, 00, 1f, 0e, 01, 05, 00, 0f, 00, 00, 20, 00, 30, 21, 01, 05, 03, 0f, 00, 03, 20, 00, 30, 00, 00, 33, 00, 41, 00, 00, 4b, 00, 5a, 1e, 01, 05, 00, 0f, 00, 05, 09, 03, 10, 00, 05, 0d, 00, 1b, 00, 02, 0d, 00, 1c, 1a, 04, 09, 05, 06, 31, 06, 05, 03, 06, 22, 04, 05, 03, 06, 3d, 04, 09, 04, 06, 2e, 05, 08, 00, 0f, 45, 01, 09, 03, 0a, 2a, 05, 09, 03, 0a, 3f, 05, 08, 00, 0f, 51, 01, 09, 00, 13, 00, 03, 0d, 00, 1d, 3a, 03, 09, 00, 13, 00, 03, 0d, 00, 1d, 87, 01, 03, 05, 00, 0f, 8f, 01, 01, 0c, 00, 13, 5d, 01, 0d, 00, 13, 8a, 01, 02, 0d, 00, 13, 82, 01, 04, 05, 02, 13, 65, 03, 0d, 00, 13, 7e, 02, 0d, 00, 13, f3, 01, 03, 05, 00, 0f, 69, 01, 0c, 00, 13, 6d, 01, 0d, 03, 0e, 75, 04, 0d, 00, 13, fb, 01, 02, 0d, 00, 17, 82, 02, 01, 14, 00, 1b, 71, 01, 15, 00, 1b, fe, 01, 02, 15, 00, 1b, f6, 01, 04, 0d, 00, 13, 7d, 03, 09, 00, 19, ee, 01, 02, 05, 00, 0f, ea, 01, 03, 09, 00, 22, 00, 02, 05, 00, 0f, 00, 03, 09, 00, 2c, 00, 02, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 65
@@ -120,31 +120,31 @@ Number of expressions: 65
 - expression 36 operands: lhs = Counter(20), rhs = Zero
 - expression 37 operands: lhs = Counter(29), rhs = Expression(61, Sub)
 - expression 38 operands: lhs = Expression(62, Add), rhs = Counter(30)
-- expression 39 operands: lhs = Zero, rhs = Expression(63, Sub)
-- expression 40 operands: lhs = Expression(64, Sub), rhs = Zero
+- expression 39 operands: lhs = Counter(28), rhs = Expression(63, Sub)
+- expression 40 operands: lhs = Expression(64, Sub), rhs = Counter(28)
 - expression 41 operands: lhs = Counter(26), rhs = Counter(27)
-- expression 42 operands: lhs = Zero, rhs = Expression(63, Sub)
-- expression 43 operands: lhs = Expression(64, Sub), rhs = Zero
+- expression 42 operands: lhs = Counter(28), rhs = Expression(63, Sub)
+- expression 43 operands: lhs = Expression(64, Sub), rhs = Counter(28)
 - expression 44 operands: lhs = Counter(26), rhs = Counter(27)
 - expression 45 operands: lhs = Counter(26), rhs = Counter(27)
-- expression 46 operands: lhs = Expression(64, Sub), rhs = Zero
+- expression 46 operands: lhs = Expression(64, Sub), rhs = Counter(28)
 - expression 47 operands: lhs = Counter(26), rhs = Counter(27)
 - expression 48 operands: lhs = Expression(62, Add), rhs = Counter(30)
-- expression 49 operands: lhs = Zero, rhs = Expression(63, Sub)
-- expression 50 operands: lhs = Expression(64, Sub), rhs = Zero
+- expression 49 operands: lhs = Counter(28), rhs = Expression(63, Sub)
+- expression 50 operands: lhs = Expression(64, Sub), rhs = Counter(28)
 - expression 51 operands: lhs = Counter(26), rhs = Counter(27)
 - expression 52 operands: lhs = Expression(60, Add), rhs = Counter(31)
 - expression 53 operands: lhs = Counter(29), rhs = Expression(61, Sub)
 - expression 54 operands: lhs = Expression(62, Add), rhs = Counter(30)
-- expression 55 operands: lhs = Zero, rhs = Expression(63, Sub)
-- expression 56 operands: lhs = Expression(64, Sub), rhs = Zero
+- expression 55 operands: lhs = Counter(28), rhs = Expression(63, Sub)
+- expression 56 operands: lhs = Expression(64, Sub), rhs = Counter(28)
 - expression 57 operands: lhs = Counter(26), rhs = Counter(27)
 - expression 58 operands: lhs = Expression(59, Sub), rhs = Zero
 - expression 59 operands: lhs = Expression(60, Add), rhs = Counter(31)
 - expression 60 operands: lhs = Counter(29), rhs = Expression(61, Sub)
 - expression 61 operands: lhs = Expression(62, Add), rhs = Counter(30)
-- expression 62 operands: lhs = Zero, rhs = Expression(63, Sub)
-- expression 63 operands: lhs = Expression(64, Sub), rhs = Zero
+- expression 62 operands: lhs = Counter(28), rhs = Expression(63, Sub)
+- expression 63 operands: lhs = Expression(64, Sub), rhs = Counter(28)
 - expression 64 operands: lhs = Counter(26), rhs = Counter(27)
 Number of file 0 mappings: 51
 - Code(Counter(0)) at (prev + 8, 1) to (start + 3, 28)
@@ -200,24 +200,24 @@ Number of file 0 mappings: 51
 - Code(Expression(31, Sub)) at (prev + 2, 13) to (start + 0, 19)
     = (((c23 + (((c20 - Zero) + c21) - c23)) - c24) - c25)
 - Code(Expression(60, Add)) at (prev + 3, 5) to (start + 0, 15)
-    = (c29 + ((Zero + ((c26 - c27) - Zero)) - c30))
+    = (c29 + ((c28 + ((c26 - c27) - c28)) - c30))
 - Code(Counter(26)) at (prev + 1, 12) to (start + 0, 19)
 - Code(Counter(27)) at (prev + 1, 13) to (start + 3, 14)
 - Code(Counter(29)) at (prev + 4, 13) to (start + 0, 19)
 - Code(Expression(62, Add)) at (prev + 2, 13) to (start + 0, 23)
-    = (Zero + ((c26 - c27) - Zero))
+    = (c28 + ((c26 - c27) - c28))
 - Code(Expression(64, Sub)) at (prev + 1, 20) to (start + 0, 27)
     = (c26 - c27)
-- Code(Zero) at (prev + 1, 21) to (start + 0, 27)
+- Code(Counter(28)) at (prev + 1, 21) to (start + 0, 27)
 - Code(Expression(63, Sub)) at (prev + 2, 21) to (start + 0, 27)
-    = ((c26 - c27) - Zero)
+    = ((c26 - c27) - c28)
 - Code(Expression(61, Sub)) at (prev + 4, 13) to (start + 0, 19)
-    = ((Zero + ((c26 - c27) - Zero)) - c30)
+    = ((c28 + ((c26 - c27) - c28)) - c30)
 - Code(Counter(31)) at (prev + 3, 9) to (start + 0, 25)
 - Code(Expression(59, Sub)) at (prev + 2, 5) to (start + 0, 15)
-    = ((c29 + ((Zero + ((c26 - c27) - Zero)) - c30)) - c31)
+    = ((c29 + ((c28 + ((c26 - c27) - c28)) - c30)) - c31)
 - Code(Expression(58, Sub)) at (prev + 3, 9) to (start + 0, 34)
-    = (((c29 + ((Zero + ((c26 - c27) - Zero)) - c30)) - c31) - Zero)
+    = (((c29 + ((c28 + ((c26 - c27) - c28)) - c30)) - c31) - Zero)
 - Code(Zero) at (prev + 2, 5) to (start + 0, 15)
 - Code(Zero) at (prev + 3, 9) to (start + 0, 44)
 - Code(Zero) at (prev + 2, 1) to (start + 0, 2)