mcdc-coverage: Add FFI MCDC Params for coverage mappings encoding

compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs

@@ -102,6 +102,7 @@ pub enum RegionKind {
 
     /// A DecisionRegion represents a top-level boolean expression and is
     /// associated with a variable length bitmap index and condition number.
+    /// FIXME(dprn): Remove unused variables.
     #[allow(dead_code)]
     MCDCDecisionRegion = 5,
 
@@ -110,6 +111,28 @@ pub enum RegionKind {
     MCDCBranchRegion = 6,
 }
 
+/// This struct provides LLVM's representation of "MCDCParameters" that may be defined for a
+/// Coverage Mapping Region.
+///
+/// Correspond to struct `llvm::coverage::CounterMappingRegion::MCDCParameters`
+///
+/// Must match The layout of `LLVMRustMCDCParameters`
+#[derive(Copy, Clone, Debug, Default)]
+#[repr(C)]
+pub struct MCDCParameters {
+    /// Byte Index of Bitmap Coverage Object for a Decision Region.
+    bitmap_idx: u32,
+
+    /// Number of Conditions used for a Decision Region.
+    num_conditions: u32,
+
+    /// IDs used to represent a branch region and other branch regions
+    /// evaluated based on True and False branches.
+    id: u32,
+    true_id: u32,
+    false_id: u32,
+}
+
 /// This struct provides LLVM's representation of a "CoverageMappingRegion", encoded into the
 /// coverage map, in accordance with the
 /// [LLVM Code Coverage Mapping Format](https://github.com/rust-lang/llvm-project/blob/rustc/13.0-2021-09-30/llvm/docs/CoverageMappingFormat.rst#llvm-code-coverage-mapping-format).
@@ -155,6 +178,8 @@ pub struct CounterMappingRegion {
     end_col: u32,
 
     kind: RegionKind,
+
+    mcdc_params: MCDCParameters,
 }
 
 impl CounterMappingRegion {
@@ -181,6 +206,7 @@ impl CounterMappingRegion {
                 start_col,
                 end_line,
                 end_col,
+                None,
             ),
         }
     }
@@ -203,9 +229,11 @@ impl CounterMappingRegion {
             end_line,
             end_col,
             kind: RegionKind::CodeRegion,
+            mcdc_params: Default::default(),
         }
     }
 
+    /// - `mcdc_params` should be None when MCDC is disabled.
     pub(crate) fn branch_region(
         counter: Counter,
         false_counter: Counter,
@@ -214,7 +242,13 @@ impl CounterMappingRegion {
         start_col: u32,
         end_line: u32,
         end_col: u32,
+        mcdc_params: Option<MCDCParameters>,
     ) -> Self {
+        let (kind, mcdc_params) = match mcdc_params {
+            None => (RegionKind::BranchRegion, Default::default()),
+            Some(params) => (RegionKind::MCDCBranchRegion, params),
+        };
+
         Self {
             counter,
             false_counter,
@@ -224,7 +258,36 @@ impl CounterMappingRegion {
             start_col,
             end_line,
             end_col,
-            kind: RegionKind::BranchRegion,
+            kind,
+            mcdc_params,
+        }
+    }
+
+    #[allow(dead_code)]
+    pub(crate) fn decision_region(
+        bitmap_idx: u32,
+        num_conditions: u32,
+        file_id: u32,
+        start_line: u32,
+        start_col: u32,
+        end_line: u32,
+        end_col: u32,
+    ) -> Self {
+        Self {
+            counter: Counter::ZERO,
+            false_counter: Counter::ZERO,
+            file_id,
+            expanded_file_id: 0,
+            start_line,
+            start_col,
+            end_line,
+            end_col,
+            kind: RegionKind::MCDCDecisionRegion,
+            mcdc_params: MCDCParameters {
+                bitmap_idx,
+                num_conditions,
+                .. Default::default()
+            },
         }
     }
 
@@ -249,6 +312,7 @@ impl CounterMappingRegion {
             end_line,
             end_col,
             kind: RegionKind::ExpansionRegion,
+            mcdc_params: Default::default(),
         }
     }
 
@@ -272,6 +336,7 @@ impl CounterMappingRegion {
             end_line,
             end_col,
             kind: RegionKind::SkippedRegion,
+            mcdc_params: Default::default(),
         }
     }
 
@@ -296,6 +361,7 @@ impl CounterMappingRegion {
             end_line,
             end_col: (1_u32 << 31) | end_col,
             kind: RegionKind::GapRegion,
+            mcdc_params: Default::default(),
         }
     }
 }

compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp

@@ -68,6 +68,30 @@ fromRust(LLVMRustCounterMappingRegionKind Kind) {
   report_fatal_error("Bad LLVMRustCounterMappingRegionKind!");
 }
 
+// FFI equivalent of struct `llvm::coverage::CounterMappingRegion::MCDCParameters`
+// https://github.com/rust-lang/llvm-project/blob/66a2881a/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h#L253-L263
+struct LLVMRustMCDCParameters {
+    /// Byte Index of Bitmap Coverage Object for a Decision Region.
+    uint32_t BitmapIdx = 0;
+
+    /// Number of Conditions used for a Decision Region.
+    uint32_t NumConditions = 0;
+
+    /// IDs used to represent a branch region and other branch regions
+    /// evaluated based on True and False branches.
+    uint32_t ID = 0;
+    uint32_t TrueID = 0;
+    uint32_t FalseID = 0;
+};
+
+static coverage::CounterMappingRegion::MCDCParameters
+fromRust(LLVMRustMCDCParameters MCDCParams) {
+  return coverage::CounterMappingRegion::MCDCParameters{
+    MCDCParams.BitmapIdx, MCDCParams.NumConditions,
+    MCDCParams.ID, MCDCParams.TrueID, MCDCParams.FalseID
+  };
+}
+
 // FFI equivalent of struct `llvm::coverage::CounterMappingRegion`
 // https://github.com/rust-lang/llvm-project/blob/ea6fa9c2/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h#L211-L304
 struct LLVMRustCounterMappingRegion {
@@ -80,6 +104,7 @@ struct LLVMRustCounterMappingRegion {
   uint32_t LineEnd;
   uint32_t ColumnEnd;
   LLVMRustCounterMappingRegionKind Kind;
+  LLVMRustMCDCParameters MCDCParams;
 };
 
 // FFI equivalent of enum `llvm::coverage::CounterExpression::ExprKind`
@@ -146,7 +171,7 @@ extern "C" void LLVMRustCoverageWriteMappingToBuffer(
     MappingRegions.emplace_back(
         fromRust(Region.Count), fromRust(Region.FalseCount),
 #if LLVM_VERSION_GE(18, 0) && LLVM_VERSION_LT(19, 0)
-        coverage::CounterMappingRegion::MCDCParameters{},
+        fromRust(Region.MCDCParams),
 #endif
         Region.FileID, Region.ExpandedFileID,
         Region.LineStart, Region.ColumnStart, Region.LineEnd, Region.ColumnEnd,