coverage: Regression test for ICE triggered by self-loops

tests/coverage/let_else_loop.cov-map

@@ -0,0 +1,30 @@
+Function name: let_else_loop::_if (unused)
+Raw bytes (19): 0x[01, 01, 00, 03, 00, 16, 01, 01, 0c, 00, 02, 09, 00, 10, 00, 02, 09, 00, 10]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 3
+- Code(Zero) at (prev + 22, 1) to (start + 1, 12)
+- Code(Zero) at (prev + 2, 9) to (start + 0, 16)
+- Code(Zero) at (prev + 2, 9) to (start + 0, 16)
+
+Function name: let_else_loop::_loop_either_way (unused)
+Raw bytes (19): 0x[01, 01, 00, 03, 00, 0f, 01, 01, 14, 00, 01, 1c, 00, 23, 00, 01, 05, 00, 0c]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 3
+- Code(Zero) at (prev + 15, 1) to (start + 1, 20)
+- Code(Zero) at (prev + 1, 28) to (start + 0, 35)
+- Code(Zero) at (prev + 1, 5) to (start + 0, 12)
+
+Function name: let_else_loop::loopy
+Raw bytes (19): 0x[01, 01, 00, 03, 01, 09, 01, 01, 14, 00, 01, 1c, 00, 23, 05, 01, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 3
+- Code(Counter(0)) at (prev + 9, 1) to (start + 1, 20)
+- Code(Zero) at (prev + 1, 28) to (start + 0, 35)
+- Code(Counter(1)) at (prev + 1, 1) to (start + 0, 2)
+

tests/coverage/let_else_loop.coverage

@@ -0,0 +1,35 @@
+   LL|       |#![feature(coverage_attribute)]
+   LL|       |//@ edition: 2021
+   LL|       |//@ ignore-test
+   LL|       |// Regression test for <https://github.com/rust-lang/rust/issues/122738>.
+   LL|       |// These code patterns should not trigger an ICE when allocating a physical
+   LL|       |// counter to a node and also one of its in-edges, because that is allowed
+   LL|       |// when the node contains a tight loop to itself.
+   LL|       |
+   LL|      1|fn loopy(cond: bool) {
+   LL|      1|    let true = cond else { loop {} };
+                                         ^0
+   LL|      1|}
+   LL|       |
+   LL|       |// Variant that also has `loop {}` on the success path.
+   LL|       |// This isn't needed to catch the original ICE, but might help detect regressions.
+   LL|      0|fn _loop_either_way(cond: bool) {
+   LL|      0|    let true = cond else { loop {} };
+   LL|      0|    loop {}
+   LL|       |}
+   LL|       |
+   LL|       |// Variant using regular `if` instead of let-else.
+   LL|       |// This doesn't trigger the original ICE, but might help detect regressions.
+   LL|      0|fn _if(cond: bool) {
+   LL|      0|    if cond {
+   LL|      0|        loop {}
+   LL|       |    } else {
+   LL|      0|        loop {}
+   LL|       |    }
+   LL|       |}
+   LL|       |
+   LL|       |#[coverage(off)]
+   LL|       |fn main() {
+   LL|       |    loopy(true);
+   LL|       |}
+

tests/coverage/let_else_loop.rs

@@ -0,0 +1,33 @@
+#![feature(coverage_attribute)]
+//@ edition: 2021
+//@ ignore-test
+// Regression test for <https://github.com/rust-lang/rust/issues/122738>.
+// These code patterns should not trigger an ICE when allocating a physical
+// counter to a node and also one of its in-edges, because that is allowed
+// when the node contains a tight loop to itself.
+
+fn loopy(cond: bool) {
+    let true = cond else { loop {} };
+}
+
+// Variant that also has `loop {}` on the success path.
+// This isn't needed to catch the original ICE, but might help detect regressions.
+fn _loop_either_way(cond: bool) {
+    let true = cond else { loop {} };
+    loop {}
+}
+
+// Variant using regular `if` instead of let-else.
+// This doesn't trigger the original ICE, but might help detect regressions.
+fn _if(cond: bool) {
+    if cond {
+        loop {}
+    } else {
+        loop {}
+    }
+}
+
+#[coverage(off)]
+fn main() {
+    loopy(true);
+}