Implement Modified Condition/Decision Coverage

compiler/rustc_codegen_llvm/src/builder.rs

@@ -17,7 +17,7 @@ use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_hir::def_id::DefId;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::ty::layout::{
-    FnAbiError, FnAbiOfHelpers, FnAbiRequest, LayoutError, LayoutOfHelpers, TyAndLayout,
+    FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasTyCtxt, LayoutError, LayoutOfHelpers, TyAndLayout,
 };
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_sanitizers::{cfi, kcfi};
@@ -1702,4 +1702,128 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
         };
         kcfi_bundle
     }
+
+    pub(crate) fn mcdc_parameters(
+        &mut self,
+        fn_name: &'ll Value,
+        hash: &'ll Value,
+        bitmap_bytes: &'ll Value,
+    ) -> &'ll Value {
+        debug!("mcdc_parameters() with args ({:?}, {:?}, {:?})", fn_name, hash, bitmap_bytes);
+
+        assert!(llvm_util::get_version() >= (18, 0, 0), "MCDC intrinsics require LLVM 18 or later");
+
+        let llfn = unsafe { llvm::LLVMRustGetInstrProfMCDCParametersIntrinsic(self.cx().llmod) };
+        let llty = self.cx.type_func(
+            &[self.cx.type_ptr(), self.cx.type_i64(), self.cx.type_i32()],
+            self.cx.type_void(),
+        );
+        let args = &[fn_name, hash, bitmap_bytes];
+        let args = self.check_call("call", llty, llfn, args);
+
+        unsafe {
+            let _ = llvm::LLVMRustBuildCall(
+                self.llbuilder,
+                llty,
+                llfn,
+                args.as_ptr() as *const &llvm::Value,
+                args.len() as c_uint,
+                [].as_ptr(),
+                0 as c_uint,
+            );
+            // Create condition bitmap named `mcdc.addr`.
+            let mut bx = Builder::with_cx(self.cx);
+            bx.position_at_start(llvm::LLVMGetFirstBasicBlock(self.llfn()));
+            let cond_bitmap = {
+                let alloca =
+                    llvm::LLVMBuildAlloca(bx.llbuilder, bx.cx.type_i32(), c"mcdc.addr".as_ptr());
+                llvm::LLVMSetAlignment(alloca, 4);
+                alloca
+            };
+            bx.store(self.const_i32(0), cond_bitmap, self.tcx().data_layout.i32_align.abi);
+            cond_bitmap
+        }
+    }
+
+    pub(crate) fn mcdc_tvbitmap_update(
+        &mut self,
+        fn_name: &'ll Value,
+        hash: &'ll Value,
+        bitmap_bytes: &'ll Value,
+        bitmap_index: &'ll Value,
+        mcdc_temp: &'ll Value,
+    ) {
+        debug!(
+            "mcdc_tvbitmap_update() with args ({:?}, {:?}, {:?}, {:?}, {:?})",
+            fn_name, hash, bitmap_bytes, bitmap_index, mcdc_temp
+        );
+        assert!(llvm_util::get_version() >= (18, 0, 0), "MCDC intrinsics require LLVM 18 or later");
+
+        let llfn =
+            unsafe { llvm::LLVMRustGetInstrProfMCDCTVBitmapUpdateIntrinsic(self.cx().llmod) };
+        let llty = self.cx.type_func(
+            &[
+                self.cx.type_ptr(),
+                self.cx.type_i64(),
+                self.cx.type_i32(),
+                self.cx.type_i32(),
+                self.cx.type_ptr(),
+            ],
+            self.cx.type_void(),
+        );
+        let args = &[fn_name, hash, bitmap_bytes, bitmap_index, mcdc_temp];
+        let args = self.check_call("call", llty, llfn, args);
+        unsafe {
+            let _ = llvm::LLVMRustBuildCall(
+                self.llbuilder,
+                llty,
+                llfn,
+                args.as_ptr() as *const &llvm::Value,
+                args.len() as c_uint,
+                [].as_ptr(),
+                0 as c_uint,
+            );
+        }
+        let i32_align = self.tcx().data_layout.i32_align.abi;
+        self.store(self.const_i32(0), mcdc_temp, i32_align);
+    }
+
+    pub(crate) fn mcdc_condbitmap_update(
+        &mut self,
+        fn_name: &'ll Value,
+        hash: &'ll Value,
+        cond_loc: &'ll Value,
+        mcdc_temp: &'ll Value,
+        bool_value: &'ll Value,
+    ) {
+        debug!(
+            "mcdc_condbitmap_update() with args ({:?}, {:?}, {:?}, {:?}, {:?})",
+            fn_name, hash, cond_loc, mcdc_temp, bool_value
+        );
+        assert!(llvm_util::get_version() >= (18, 0, 0), "MCDC intrinsics require LLVM 18 or later");
+        let llfn = unsafe { llvm::LLVMRustGetInstrProfMCDCCondBitmapIntrinsic(self.cx().llmod) };
+        let llty = self.cx.type_func(
+            &[
+                self.cx.type_ptr(),
+                self.cx.type_i64(),
+                self.cx.type_i32(),
+                self.cx.type_ptr(),
+                self.cx.type_i1(),
+            ],
+            self.cx.type_void(),
+        );
+        let args = &[fn_name, hash, cond_loc, mcdc_temp, bool_value];
+        self.check_call("call", llty, llfn, args);
+        unsafe {
+            let _ = llvm::LLVMRustBuildCall(
+                self.llbuilder,
+                llty,
+                llfn,
+                args.as_ptr() as *const &llvm::Value,
+                args.len() as c_uint,
+                [].as_ptr(),
+                0 as c_uint,
+            );
+        }
+    }
 }

compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs

@@ -1,4 +1,6 @@
-use rustc_middle::mir::coverage::{CodeRegion, CounterId, CovTerm, ExpressionId, MappingKind};
+use rustc_middle::mir::coverage::{
+    CodeRegion, ConditionInfo, CounterId, CovTerm, DecisionInfo, ExpressionId, MappingKind,
+};
 
 /// Must match the layout of `LLVMRustCounterKind`.
 #[derive(Copy, Clone, Debug)]
@@ -99,6 +101,86 @@ pub enum RegionKind {
     /// associated with two counters, each representing the number of times the
     /// expression evaluates to true or false.
     BranchRegion = 4,
+
+    /// A DecisionRegion represents a top-level boolean expression and is
+    /// associated with a variable length bitmap index and condition number.
+    MCDCDecisionRegion = 5,
+
+    /// A Branch Region can be extended to include IDs to facilitate MC/DC.
+    MCDCBranchRegion = 6,
+}
+
+pub mod mcdc {
+    use rustc_middle::mir::coverage::{ConditionInfo, DecisionInfo};
+
+    /// Must match the layout of `LLVMRustMCDCDecisionParameters`.
+    #[repr(C)]
+    #[derive(Clone, Copy, Debug, Default)]
+    pub struct DecisionParameters {
+        bitmap_idx: u32,
+        conditions_num: u16,
+    }
+
+    // ConditionId in llvm is `unsigned int` at 18 while `int16_t` at [19](https://github.com/llvm/llvm-project/pull/81257)
+    type LLVMConditionId = i16;
+
+    /// Must match the layout of `LLVMRustMCDCBranchParameters`.
+    #[repr(C)]
+    #[derive(Clone, Copy, Debug, Default)]
+    pub struct BranchParameters {
+        condition_id: LLVMConditionId,
+        condition_ids: [LLVMConditionId; 2],
+    }
+
+    #[repr(C)]
+    #[derive(Clone, Copy, Debug)]
+    pub enum ParameterTag {
+        None = 0,
+        Decision = 1,
+        Branch = 2,
+    }
+    /// Same layout with `LLVMRustMCDCParameters`
+    #[repr(C)]
+    #[derive(Clone, Copy, Debug)]
+    pub struct Parameters {
+        tag: ParameterTag,
+        decision_params: DecisionParameters,
+        branch_params: BranchParameters,
+    }
+
+    impl Parameters {
+        pub fn none() -> Self {
+            Self {
+                tag: ParameterTag::None,
+                decision_params: Default::default(),
+                branch_params: Default::default(),
+            }
+        }
+        pub fn decision(decision_params: DecisionParameters) -> Self {
+            Self { tag: ParameterTag::Decision, decision_params, branch_params: Default::default() }
+        }
+        pub fn branch(branch_params: BranchParameters) -> Self {
+            Self { tag: ParameterTag::Branch, decision_params: Default::default(), branch_params }
+        }
+    }
+
+    impl From<ConditionInfo> for BranchParameters {
+        fn from(value: ConditionInfo) -> Self {
+            Self {
+                condition_id: value.condition_id.as_u32() as LLVMConditionId,
+                condition_ids: [
+                    value.false_next_id.as_u32() as LLVMConditionId,
+                    value.true_next_id.as_u32() as LLVMConditionId,
+                ],
+            }
+        }
+    }
+
+    impl From<DecisionInfo> for DecisionParameters {
+        fn from(value: DecisionInfo) -> Self {
+            Self { bitmap_idx: value.bitmap_idx, conditions_num: value.conditions_num }
+        }
+    }
 }
 
 /// This struct provides LLVM's representation of a "CoverageMappingRegion", encoded into the
@@ -122,6 +204,7 @@ pub struct CounterMappingRegion {
     /// for the false branch of the region.
     false_counter: Counter,
 
+    mcdc_params: mcdc::Parameters,
     /// An indirect reference to the source filename. In the LLVM Coverage Mapping Format, the
     /// file_id is an index into a function-specific `virtual_file_mapping` array of indexes
     /// that, in turn, are used to look up the filename for this region.
@@ -173,6 +256,26 @@ impl CounterMappingRegion {
                 end_line,
                 end_col,
             ),
+            MappingKind::MCDCBranch { true_term, false_term, mcdc_params } => {
+                Self::mcdc_branch_region(
+                    Counter::from_term(true_term),
+                    Counter::from_term(false_term),
+                    mcdc_params,
+                    local_file_id,
+                    start_line,
+                    start_col,
+                    end_line,
+                    end_col,
+                )
+            }
+            MappingKind::MCDCDecision(decision_info) => Self::decision_region(
+                decision_info,
+                local_file_id,
+                start_line,
+                start_col,
+                end_line,
+                end_col,
+            ),
         }
     }
 
@@ -187,6 +290,7 @@ impl CounterMappingRegion {
         Self {
             counter,
             false_counter: Counter::ZERO,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id: 0,
             start_line,
@@ -209,6 +313,7 @@ impl CounterMappingRegion {
         Self {
             counter,
             false_counter,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id: 0,
             start_line,
@@ -219,6 +324,54 @@ impl CounterMappingRegion {
         }
     }
 
+    pub(crate) fn mcdc_branch_region(
+        counter: Counter,
+        false_counter: Counter,
+        condition_info: ConditionInfo,
+        file_id: u32,
+        start_line: u32,
+        start_col: u32,
+        end_line: u32,
+        end_col: u32,
+    ) -> Self {
+        Self {
+            counter,
+            false_counter,
+            mcdc_params: mcdc::Parameters::branch(condition_info.into()),
+            file_id,
+            expanded_file_id: 0,
+            start_line,
+            start_col,
+            end_line,
+            end_col,
+            kind: RegionKind::MCDCBranchRegion,
+        }
+    }
+
+    pub(crate) fn decision_region(
+        decision_info: DecisionInfo,
+        file_id: u32,
+        start_line: u32,
+        start_col: u32,
+        end_line: u32,
+        end_col: u32,
+    ) -> Self {
+        let mcdc_params = mcdc::Parameters::decision(decision_info.into());
+
+        Self {
+            counter: Counter::ZERO,
+            false_counter: Counter::ZERO,
+            mcdc_params,
+            file_id,
+            expanded_file_id: 0,
+            start_line,
+            start_col,
+            end_line,
+            end_col,
+            kind: RegionKind::MCDCDecisionRegion,
+        }
+    }
+
     // This function might be used in the future; the LLVM API is still evolving, as is coverage
     // support.
     #[allow(dead_code)]
@@ -233,6 +386,7 @@ impl CounterMappingRegion {
         Self {
             counter: Counter::ZERO,
             false_counter: Counter::ZERO,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id,
             start_line,
@@ -256,6 +410,7 @@ impl CounterMappingRegion {
         Self {
             counter: Counter::ZERO,
             false_counter: Counter::ZERO,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id: 0,
             start_line,
@@ -280,6 +435,7 @@ impl CounterMappingRegion {
         Self {
             counter,
             false_counter: Counter::ZERO,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id: 0,
             start_line,