Rollup merge of #119208 - Zalathar:hoist, r=WaffleLapkin,Swatinem

coverage: Hoist some complex code out of the main span refinement loop

The span refinement loop in `spans.rs` takes the spans that have been extracted from MIR, and modifies them to produce more helpful output in coverage reports.

It is also one of the most complicated pieces of code in the coverage instrumentor. It has an abundance of moving pieces that make it difficult to understand, and most attempts to modify it end up accidentally changing its behaviour in unacceptable ways.

This PR nevertheless tries to make a dent in it by hoisting two pieces of special-case logic out of the main loop, and into separate preprocessing passes. Coverage tests show that the resulting mappings are *almost* identical, with all known differences being unimportant.

This should hopefully unlock further simplifications to the refinement loop, since it now has fewer edge cases to worry about.

3 files changed, 21 insertions, 27 deletions

diff --git a/tests/coverage/closure.cov-map b/tests/coverage/closure.cov-map
index 522c1e73afe..c5ac17600cd 100644
--- a/tests/coverage/closure.cov-map
+++ b/tests/coverage/closure.cov-map
@@ -81,21 +81,18 @@ Number of file 0 mappings: 1
 - Code(Zero) at (prev + 171, 13) to (start + 2, 14)
 
 Function name: closure::main::{closure#14}
-Raw bytes (36): 0x[01, 01, 03, 05, 0a, 01, 05, 01, 05, 05, 03, b2, 01, 0d, 00, 15, 01, 01, 11, 01, 1b, 05, 01, 1e, 00, 25, 0a, 00, 2f, 00, 33, 03, 01, 0d, 00, 0e]
+Raw bytes (29): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, b2, 01, 0d, 02, 1b, 05, 02, 1e, 00, 25, 02, 00, 2f, 00, 33, 07, 01, 0d, 00, 0e]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 3
-- expression 0 operands: lhs = Counter(1), rhs = Expression(2, Sub)
-- expression 1 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 2 operands: lhs = Counter(0), rhs = Counter(1)
-Number of file 0 mappings: 5
-- Code(Expression(0, Add)) at (prev + 178, 13) to (start + 0, 21)
-    = (c1 + (c0 - c1))
-- Code(Counter(0)) at (prev + 1, 17) to (start + 1, 27)
-- Code(Counter(1)) at (prev + 1, 30) to (start + 0, 37)
-- Code(Expression(2, Sub)) at (prev + 0, 47) to (start + 0, 51)
+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(Counter(0)) at (prev + 178, 13) to (start + 2, 27)
+- Code(Counter(1)) at (prev + 2, 30) to (start + 0, 37)
+- Code(Expression(0, Sub)) at (prev + 0, 47) to (start + 0, 51)
     = (c0 - c1)
-- Code(Expression(0, Add)) at (prev + 1, 13) to (start + 0, 14)
+- Code(Expression(1, Add)) at (prev + 1, 13) to (start + 0, 14)
     = (c1 + (c0 - c1))
 
 Function name: closure::main::{closure#15}
@@ -118,21 +115,18 @@ Number of file 0 mappings: 6
     = (c1 + (c0 - c1))
 
 Function name: closure::main::{closure#16}
-Raw bytes (36): 0x[01, 01, 03, 05, 0a, 01, 05, 01, 05, 05, 03, c4, 01, 0d, 00, 15, 01, 01, 11, 01, 1b, 05, 01, 1e, 00, 25, 0a, 00, 2f, 00, 33, 03, 01, 0d, 00, 0e]
+Raw bytes (29): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, c4, 01, 0d, 02, 1b, 05, 02, 1e, 00, 25, 02, 00, 2f, 00, 33, 07, 01, 0d, 00, 0e]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 3
-- expression 0 operands: lhs = Counter(1), rhs = Expression(2, Sub)
-- expression 1 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 2 operands: lhs = Counter(0), rhs = Counter(1)
-Number of file 0 mappings: 5
-- Code(Expression(0, Add)) at (prev + 196, 13) to (start + 0, 21)
-    = (c1 + (c0 - c1))
-- Code(Counter(0)) at (prev + 1, 17) to (start + 1, 27)
-- Code(Counter(1)) at (prev + 1, 30) to (start + 0, 37)
-- Code(Expression(2, Sub)) at (prev + 0, 47) to (start + 0, 51)
+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(Counter(0)) at (prev + 196, 13) to (start + 2, 27)
+- Code(Counter(1)) at (prev + 2, 30) to (start + 0, 37)
+- Code(Expression(0, Sub)) at (prev + 0, 47) to (start + 0, 51)
     = (c0 - c1)
-- Code(Expression(0, Add)) at (prev + 1, 13) to (start + 0, 14)
+- Code(Expression(1, Add)) at (prev + 1, 13) to (start + 0, 14)
     = (c1 + (c0 - c1))
 
 Function name: closure::main::{closure#17}
diff --git a/tests/coverage/inline-dead.cov-map b/tests/coverage/inline-dead.cov-map
index 958b423f24c..ab04e746b91 100644
--- a/tests/coverage/inline-dead.cov-map
+++ b/tests/coverage/inline-dead.cov-map
@@ -31,14 +31,14 @@ Number of file 0 mappings: 2
 - Code(Counter(0)) at (prev + 7, 6) to (start + 2, 2)
 
 Function name: inline_dead::main::{closure#0}
-Raw bytes (23): 0x[01, 01, 02, 00, 06, 01, 00, 03, 01, 07, 17, 00, 18, 00, 02, 0d, 00, 0e, 03, 02, 05, 00, 06]
+Raw bytes (23): 0x[01, 01, 02, 00, 06, 01, 00, 03, 01, 07, 17, 01, 16, 00, 02, 0d, 00, 0e, 03, 02, 05, 00, 06]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 2
 - expression 0 operands: lhs = Zero, rhs = Expression(1, Sub)
 - expression 1 operands: lhs = Counter(0), rhs = Zero
 Number of file 0 mappings: 3
-- Code(Counter(0)) at (prev + 7, 23) to (start + 0, 24)
+- Code(Counter(0)) at (prev + 7, 23) to (start + 1, 22)
 - Code(Zero) at (prev + 2, 13) to (start + 0, 14)
 - Code(Expression(0, Add)) at (prev + 2, 5) to (start + 0, 6)
     = (Zero + (c0 - Zero))
diff --git a/tests/coverage/inline-dead.coverage b/tests/coverage/inline-dead.coverage
index de96aa17acd..7c201f482db 100644
--- a/tests/coverage/inline-dead.coverage
+++ b/tests/coverage/inline-dead.coverage
@@ -5,7 +5,7 @@
    LL|      1|    println!("{}", live::<false>());
    LL|      1|
    LL|      1|    let f = |x: bool| {
-   LL|       |        debug_assert!(
+   LL|      1|        debug_assert!(
    LL|      0|            x
    LL|       |        );
    LL|      1|    };