Auto merge of #126733 - ZhuUx:llvm-19-adapt, r=Zalathar

[Coverage][MCDC] Adapt mcdc to llvm 19

Related issue: #126672

Also finish task 4 at #124144

[llvm #82448](https://github.com/llvm/llvm-project/pull/82448) has introduced some break changes into mcdc, causing incompatibility between llvm 18 and 19. This draft adapts to that change and gives up supporting for llvm-18.

1 files changed, 14 insertions, 31 deletions

diff --git a/compiler/rustc_middle/src/mir/coverage.rs b/compiler/rustc_middle/src/mir/coverage.rs
index bfe2a2c2cb3..4a876dc1228 100644
--- a/compiler/rustc_middle/src/mir/coverage.rs
+++ b/compiler/rustc_middle/src/mir/coverage.rs
@@ -67,7 +67,7 @@ rustc_index::newtype_index! {
 }
 
 impl ConditionId {
-    pub const NONE: Self = Self::from_u32(0);
+    pub const START: Self = Self::from_usize(0);
 }
 
 /// Enum that can hold a constant zero value, the ID of an physical coverage
@@ -128,8 +128,8 @@ pub enum CoverageKind {
 
     /// Marks the point in MIR control flow represented by a evaluated condition.
     ///
-    /// This is eventually lowered to `llvm.instrprof.mcdc.condbitmap.update` in LLVM IR.
-    CondBitmapUpdate { id: ConditionId, value: bool, decision_depth: u16 },
+    /// This is eventually lowered to instruments updating mcdc temp variables.
+    CondBitmapUpdate { index: u32, decision_depth: u16 },
 
     /// Marks the point in MIR control flow represented by a evaluated decision.
     ///
@@ -145,14 +145,8 @@ impl Debug for CoverageKind {
             BlockMarker { id } => write!(fmt, "BlockMarker({:?})", id.index()),
             CounterIncrement { id } => write!(fmt, "CounterIncrement({:?})", id.index()),
             ExpressionUsed { id } => write!(fmt, "ExpressionUsed({:?})", id.index()),
-            CondBitmapUpdate { id, value, decision_depth } => {
-                write!(
-                    fmt,
-                    "CondBitmapUpdate({:?}, {:?}, depth={:?})",
-                    id.index(),
-                    value,
-                    decision_depth
-                )
+            CondBitmapUpdate { index, decision_depth } => {
+                write!(fmt, "CondBitmapUpdate(index={:?}, depth={:?})", index, decision_depth)
             }
             TestVectorBitmapUpdate { bitmap_idx, decision_depth } => {
                 write!(fmt, "TestVectorUpdate({:?}, depth={:?})", bitmap_idx, decision_depth)
@@ -253,7 +247,7 @@ pub struct Mapping {
 pub struct FunctionCoverageInfo {
     pub function_source_hash: u64,
     pub num_counters: usize,
-    pub mcdc_bitmap_bytes: u32,
+    pub mcdc_bitmap_bits: usize,
     pub expressions: IndexVec<ExpressionId, Expression>,
     pub mappings: Vec<Mapping>,
     /// The depth of the deepest decision is used to know how many
@@ -275,8 +269,10 @@ pub struct CoverageInfoHi {
     /// data structures without having to scan the entire body first.
     pub num_block_markers: usize,
     pub branch_spans: Vec<BranchSpan>,
-    pub mcdc_branch_spans: Vec<MCDCBranchSpan>,
-    pub mcdc_decision_spans: Vec<MCDCDecisionSpan>,
+    /// Branch spans generated by mcdc. Because of some limits mcdc builder give up generating
+    /// decisions including them so that they are handled as normal branch spans.
+    pub mcdc_degraded_branch_spans: Vec<MCDCBranchSpan>,
+    pub mcdc_spans: Vec<(MCDCDecisionSpan, Vec<MCDCBranchSpan>)>,
 }
 
 #[derive(Clone, Debug)]
@@ -291,30 +287,17 @@ pub struct BranchSpan {
 #[derive(TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
 pub struct ConditionInfo {
     pub condition_id: ConditionId,
-    pub true_next_id: ConditionId,
-    pub false_next_id: ConditionId,
-}
-
-impl Default for ConditionInfo {
-    fn default() -> Self {
-        Self {
-            condition_id: ConditionId::NONE,
-            true_next_id: ConditionId::NONE,
-            false_next_id: ConditionId::NONE,
-        }
-    }
+    pub true_next_id: Option<ConditionId>,
+    pub false_next_id: Option<ConditionId>,
 }
 
 #[derive(Clone, Debug)]
 #[derive(TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
 pub struct MCDCBranchSpan {
     pub span: Span,
-    /// If `None`, this actually represents a normal branch span inserted for
-    /// code that was too complex for MC/DC.
-    pub condition_info: Option<ConditionInfo>,
+    pub condition_info: ConditionInfo,
     pub true_marker: BlockMarkerId,
     pub false_marker: BlockMarkerId,
-    pub decision_depth: u16,
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -328,7 +311,7 @@ pub struct DecisionInfo {
 #[derive(TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
 pub struct MCDCDecisionSpan {
     pub span: Span,
-    pub num_conditions: usize,
     pub end_markers: Vec<BlockMarkerId>,
     pub decision_depth: u16,
+    pub num_conditions: usize,
 }