coverage: Add debugging flag `-Zcoverage-options=no-mir-spans`

When set, this flag skips the code that normally extracts coverage spans from
MIR statements and terminators. That sometimes makes it easier to debug branch
coverage and MC/DC coverage, because the coverage output is less noisy.

For internal debugging only. If other code changes would make it hard to keep
supporting this flag, remove it.

3 files changed, 191 insertions, 0 deletions

diff --git a/tests/coverage/branch/no-mir-spans.cov-map b/tests/coverage/branch/no-mir-spans.cov-map
new file mode 100644
index 00000000000..cb19211913f
--- /dev/null
+++ b/tests/coverage/branch/no-mir-spans.cov-map
@@ -0,0 +1,52 @@
+Function name: no_mir_spans::while_cond
+Raw bytes (16): 0x[01, 01, 00, 02, 01, 10, 01, 00, 11, 20, 05, 09, 04, 0b, 00, 10]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 2
+- Code(Counter(0)) at (prev + 16, 1) to (start + 0, 17)
+- Branch { true: Counter(1), false: Counter(2) } at (prev + 4, 11) to (start + 0, 16)
+    true  = c1
+    false = c2
+
+Function name: no_mir_spans::while_cond_not
+Raw bytes (16): 0x[01, 01, 00, 02, 01, 19, 01, 00, 15, 20, 09, 05, 04, 0b, 00, 14]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 2
+- Code(Counter(0)) at (prev + 25, 1) to (start + 0, 21)
+- Branch { true: Counter(2), false: Counter(1) } at (prev + 4, 11) to (start + 0, 20)
+    true  = c2
+    false = c1
+
+Function name: no_mir_spans::while_op_and
+Raw bytes (25): 0x[01, 01, 01, 09, 0d, 03, 01, 22, 01, 00, 13, 20, 09, 05, 05, 0b, 00, 10, 20, 02, 0d, 00, 14, 00, 19]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 1
+- expression 0 operands: lhs = Counter(2), rhs = Counter(3)
+Number of file 0 mappings: 3
+- Code(Counter(0)) at (prev + 34, 1) to (start + 0, 19)
+- Branch { true: Counter(2), false: Counter(1) } at (prev + 5, 11) to (start + 0, 16)
+    true  = c2
+    false = c1
+- Branch { true: Expression(0, Sub), false: Counter(3) } at (prev + 0, 20) to (start + 0, 25)
+    true  = (c2 - c3)
+    false = c3
+
+Function name: no_mir_spans::while_op_or
+Raw bytes (25): 0x[01, 01, 01, 09, 0d, 03, 01, 2d, 01, 00, 12, 20, 05, 09, 05, 0b, 00, 10, 20, 0d, 02, 00, 14, 00, 19]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 1
+- expression 0 operands: lhs = Counter(2), rhs = Counter(3)
+Number of file 0 mappings: 3
+- Code(Counter(0)) at (prev + 45, 1) to (start + 0, 18)
+- Branch { true: Counter(1), false: Counter(2) } at (prev + 5, 11) to (start + 0, 16)
+    true  = c1
+    false = c2
+- Branch { true: Counter(3), false: Expression(0, Sub) } at (prev + 0, 20) to (start + 0, 25)
+    true  = c3
+    false = (c2 - c3)
+
diff --git a/tests/coverage/branch/no-mir-spans.coverage b/tests/coverage/branch/no-mir-spans.coverage
new file mode 100644
index 00000000000..2cae98ed3ff
--- /dev/null
+++ b/tests/coverage/branch/no-mir-spans.coverage
@@ -0,0 +1,77 @@
+   LL|       |#![feature(coverage_attribute)]
+   LL|       |//@ edition: 2021
+   LL|       |//@ compile-flags: -Zcoverage-options=branch,no-mir-spans
+   LL|       |//@ llvm-cov-flags: --show-branches=count
+   LL|       |
+   LL|       |// Tests the behaviour of the `-Zcoverage-options=no-mir-spans` debugging flag.
+   LL|       |// The actual code below is just some non-trivial code copied from another test
+   LL|       |// (`while.rs`), and has no particular significance.
+   LL|       |
+   LL|       |macro_rules! no_merge {
+   LL|       |    () => {
+   LL|       |        for _ in 0..1 {}
+   LL|       |    };
+   LL|       |}
+   LL|       |
+   LL|      1|fn while_cond() {
+   LL|       |    no_merge!();
+   LL|       |
+   LL|       |    let mut a = 8;
+   LL|       |    while a > 0 {
+  ------------------
+  |  Branch (LL:11): [True: 8, False: 1]
+  ------------------
+   LL|       |        a -= 1;
+   LL|       |    }
+   LL|       |}
+   LL|       |
+   LL|      1|fn while_cond_not() {
+   LL|       |    no_merge!();
+   LL|       |
+   LL|       |    let mut a = 8;
+   LL|       |    while !(a == 0) {
+  ------------------
+  |  Branch (LL:11): [True: 8, False: 1]
+  ------------------
+   LL|       |        a -= 1;
+   LL|       |    }
+   LL|       |}
+   LL|       |
+   LL|      1|fn while_op_and() {
+   LL|       |    no_merge!();
+   LL|       |
+   LL|       |    let mut a = 8;
+   LL|       |    let mut b = 4;
+   LL|       |    while a > 0 && b > 0 {
+  ------------------
+  |  Branch (LL:11): [True: 5, False: 0]
+  |  Branch (LL:20): [True: 4, False: 1]
+  ------------------
+   LL|       |        a -= 1;
+   LL|       |        b -= 1;
+   LL|       |    }
+   LL|       |}
+   LL|       |
+   LL|      1|fn while_op_or() {
+   LL|       |    no_merge!();
+   LL|       |
+   LL|       |    let mut a = 4;
+   LL|       |    let mut b = 8;
+   LL|       |    while a > 0 || b > 0 {
+  ------------------
+  |  Branch (LL:11): [True: 4, False: 5]
+  |  Branch (LL:20): [True: 4, False: 1]
+  ------------------
+   LL|       |        a -= 1;
+   LL|       |        b -= 1;
+   LL|       |    }
+   LL|       |}
+   LL|       |
+   LL|       |#[coverage(off)]
+   LL|       |fn main() {
+   LL|       |    while_cond();
+   LL|       |    while_cond_not();
+   LL|       |    while_op_and();
+   LL|       |    while_op_or();
+   LL|       |}
+
diff --git a/tests/coverage/branch/no-mir-spans.rs b/tests/coverage/branch/no-mir-spans.rs
new file mode 100644
index 00000000000..acb268f2d45
--- /dev/null
+++ b/tests/coverage/branch/no-mir-spans.rs
@@ -0,0 +1,62 @@
+#![feature(coverage_attribute)]
+//@ edition: 2021
+//@ compile-flags: -Zcoverage-options=branch,no-mir-spans
+//@ llvm-cov-flags: --show-branches=count
+
+// Tests the behaviour of the `-Zcoverage-options=no-mir-spans` debugging flag.
+// The actual code below is just some non-trivial code copied from another test
+// (`while.rs`), and has no particular significance.
+
+macro_rules! no_merge {
+    () => {
+        for _ in 0..1 {}
+    };
+}
+
+fn while_cond() {
+    no_merge!();
+
+    let mut a = 8;
+    while a > 0 {
+        a -= 1;
+    }
+}
+
+fn while_cond_not() {
+    no_merge!();
+
+    let mut a = 8;
+    while !(a == 0) {
+        a -= 1;
+    }
+}
+
+fn while_op_and() {
+    no_merge!();
+
+    let mut a = 8;
+    let mut b = 4;
+    while a > 0 && b > 0 {
+        a -= 1;
+        b -= 1;
+    }
+}
+
+fn while_op_or() {
+    no_merge!();
+
+    let mut a = 4;
+    let mut b = 8;
+    while a > 0 || b > 0 {
+        a -= 1;
+        b -= 1;
+    }
+}
+
+#[coverage(off)]
+fn main() {
+    while_cond();
+    while_cond_not();
+    while_op_and();
+    while_op_or();
+}