coverage. Fix panic when generating mcdc code for inlined functions

Author: zhuyunxing

compiler/rustc_mir_transform/src/inline.rs

@@ -41,6 +41,12 @@ struct CallSite<'tcx> {
 
 impl<'tcx> MirPass<'tcx> for Inline {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
+        // FIXME(#127234): Coverage instrumentation currently doesn't handle inlined
+        // MIR correctly when Modified Condition/Decision Coverage is enabled.
+        if sess.instrument_coverage_mcdc() {
+            return false;
+        }
+
         if let Some(enabled) = sess.opts.unstable_opts.inline_mir {
             return enabled;
         }

tests/coverage/mcdc/inlined_expressions.cov-map

@@ -0,0 +1,21 @@
+Function name: inlined_expressions::inlined_instance
+Raw bytes (52): 0x[01, 01, 03, 01, 05, 0b, 02, 09, 0d, 06, 01, 08, 01, 01, 06, 28, 00, 02, 01, 05, 00, 0b, 30, 05, 02, 01, 02, 00, 00, 05, 00, 06, 05, 00, 0a, 00, 0b, 30, 09, 0d, 02, 00, 00, 00, 0a, 00, 0b, 07, 01, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 3
+- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 1 operands: lhs = Expression(2, Add), rhs = Expression(0, Sub)
+- expression 2 operands: lhs = Counter(2), rhs = Counter(3)
+Number of file 0 mappings: 6
+- Code(Counter(0)) at (prev + 8, 1) to (start + 1, 6)
+- MCDCDecision { bitmap_idx: 0, conditions_num: 2 } at (prev + 1, 5) to (start + 0, 11)
+- MCDCBranch { true: Counter(1), false: Expression(0, Sub), condition_id: 1, true_next_id: 2, false_next_id: 0 } at (prev + 0, 5) to (start + 0, 6)
+    true  = c1
+    false = (c0 - c1)
+- Code(Counter(1)) at (prev + 0, 10) to (start + 0, 11)
+- MCDCBranch { true: Counter(2), false: Counter(3), condition_id: 2, true_next_id: 0, false_next_id: 0 } at (prev + 0, 10) to (start + 0, 11)
+    true  = c2
+    false = c3
+- Code(Expression(1, Add)) at (prev + 1, 1) to (start + 0, 2)
+    = ((c2 + c3) + (c0 - c1))
+

tests/coverage/mcdc/inlined_expressions.coverage

@@ -0,0 +1,41 @@
+   LL|       |#![feature(coverage_attribute)]
+   LL|       |//@ edition: 2021
+   LL|       |//@ min-llvm-version: 18
+   LL|       |//@ compile-flags: -Zcoverage-options=mcdc -Copt-level=z -Cllvm-args=--inline-threshold=0
+   LL|       |//@ llvm-cov-flags: --show-branches=count --show-mcdc
+   LL|       |
+   LL|       |#[inline(always)]
+   LL|      3|fn inlined_instance(a: bool, b: bool) -> bool {
+   LL|      3|    a && b
+                       ^2
+  ------------------
+  |  Branch (LL:5): [True: 2, False: 1]
+  |  Branch (LL:10): [True: 1, False: 1]
+  ------------------
+  |---> MC/DC Decision Region (LL:5) to (LL:11)
+  |
+  |  Number of Conditions: 2
+  |     Condition C1 --> (LL:5)
+  |     Condition C2 --> (LL:10)
+  |
+  |  Executed MC/DC Test Vectors:
+  |
+  |     C1, C2    Result
+  |  1 { F,  -  = F      }
+  |  2 { T,  F  = F      }
+  |  3 { T,  T  = T      }
+  |
+  |  C1-Pair: covered: (1,3)
+  |  C2-Pair: covered: (2,3)
+  |  MC/DC Coverage for Decision: 100.00%
+  |
+  ------------------
+   LL|      3|}
+   LL|       |
+   LL|       |#[coverage(off)]
+   LL|       |fn main() {
+   LL|       |    let _ = inlined_instance(true, false);
+   LL|       |    let _ = inlined_instance(false, true);
+   LL|       |    let _ = inlined_instance(true, true);
+   LL|       |}
+

tests/coverage/mcdc/inlined_expressions.rs

@@ -0,0 +1,17 @@
+#![feature(coverage_attribute)]
+//@ edition: 2021
+//@ min-llvm-version: 18
+//@ compile-flags: -Zcoverage-options=mcdc -Copt-level=z -Cllvm-args=--inline-threshold=0
+//@ llvm-cov-flags: --show-branches=count --show-mcdc
+
+#[inline(always)]
+fn inlined_instance(a: bool, b: bool) -> bool {
+    a && b
+}
+
+#[coverage(off)]
+fn main() {
+    let _ = inlined_instance(true, false);
+    let _ = inlined_instance(false, true);
+    let _ = inlined_instance(true, true);
+}