feat: implement validation pass and supporting infrastructure

This commit implements the following:

* The `Rule` trait, used to implement validation rules for different
  types of IR items
* The `ModuleValidator` pass, used to run a suite of validations against
  modules and the functions they contain
* A suite of validation rules for things critical areas where we want to
  catch errors in the IR before attempting to process it for code
  generation: naming conventions, function signatures, ensuring blocks
  are valid, and that key properties of the SSA representation are
  upheld, such as value uses being dominated by their definitions, as
  well as a typechecking rule.

hir-analysis/src/lib.rs

@@ -2,11 +2,13 @@ mod control_flow;
 mod dominance;
 mod liveness;
 mod loops;
+mod validation;
 
 pub use self::control_flow::{BlockPredecessor, ControlFlowGraph};
 pub use self::dominance::{DominanceFrontier, DominatorTree, DominatorTreePreorder};
 pub use self::liveness::LivenessAnalysis;
 pub use self::loops::{Loop, LoopAnalysis, LoopLevel};
+pub use self::validation::{ModuleValidator, Rule};
 
 use anyhow::anyhow;
 
@@ -164,11 +166,15 @@ impl FunctionAnalysis {
     pub fn cfg_changed(&mut self, function: &miden_hir::Function) {
         // If the dominator tree hasn't been computed, no other
         // analyses could possibly have been computed yet.
-        let Some(domtree) = self.domtree.as_mut() else { return; };
+        let Some(domtree) = self.domtree.as_mut() else {
+            return;
+        };
         domtree.compute(function, &self.cfg);
 
         // Likewise for loop analysis - we can't compute liveness without it
-        let Some(loops) = self.loops.as_mut() else { return; };
+        let Some(loops) = self.loops.as_mut() else {
+            return;
+        };
         loops.compute(function, &self.cfg, domtree);
 
         if let Some(liveness) = self.liveness.as_mut() {

hir-analysis/src/validation/block.rs

@@ -0,0 +1,243 @@
+use miden_diagnostics::{DiagnosticsHandler, Severity, SourceSpan, Spanned};
+use miden_hir::*;
+use rustc_hash::FxHashSet;
+use smallvec::SmallVec;
+
+use super::{Rule, ValidationError};
+use crate::DominatorTree;
+
+/// This validation rule ensures that all values definitions dominate their uses.
+///
+/// For example, it is not valid to use a value in a block when its definition only
+/// occurs along a subset of control flow paths which may be taken to that block.
+///
+/// This also catches uses of values which are orphaned (i.e. they are defined by
+/// a block parameter or instruction which is not attached to the function).
+pub struct DefsDominateUses<'a> {
+    dfg: &'a DataFlowGraph,
+    domtree: &'a DominatorTree,
+}
+impl<'a> DefsDominateUses<'a> {
+    pub fn new(dfg: &'a DataFlowGraph, domtree: &'a DominatorTree) -> Self {
+        Self { dfg, domtree }
+    }
+}
+impl<'a> Rule<BlockData> for DefsDominateUses<'a> {
+    fn validate(
+        &mut self,
+        block_data: &BlockData,
+        diagnostics: &DiagnosticsHandler,
+    ) -> Result<(), ValidationError> {
+        let current_block = block_data.id;
+        let mut uses = FxHashSet::<Value>::default();
+        let mut defs = FxHashSet::<Value>::default();
+        for node in block_data.insts.iter() {
+            let span = node.span();
+
+            uses.clear();
+            defs.clear();
+
+            // Verify the integrity of the instruction results
+            for result in self.dfg.inst_results(node.key) {
+                // It should never be possible for a value id to be present in the result set twice
+                assert!(defs.insert(*result));
+            }
+
+            // Gather all value uses to check
+            uses.extend(node.arguments(&self.dfg.value_lists).iter().copied());
+            match node.analyze_branch(&self.dfg.value_lists) {
+                BranchInfo::NotABranch => (),
+                BranchInfo::SingleDest(_, args) => {
+                    uses.extend(args.iter().copied());
+                }
+                BranchInfo::MultiDest(ref jts) => {
+                    for jt in jts.iter() {
+                        uses.extend(jt.args.iter().copied());
+                    }
+                }
+            }
+
+            // Make sure there are no uses of the instructions own results
+            if !defs.is_disjoint(&uses) {
+                invalid_instruction!(
+                    diagnostics,
+                    node.key,
+                    span,
+                    "an instruction may not use its own results as arguments",
+                    "This situation can only arise if one has manually modified the arguments of an instruction, \
+                     incorrectly inserting a value obtained from the set of instruction results."
+                );
+            }
+
+            // Next, ensure that all used values are dominated by their definition
+            for value in uses.iter().copied() {
+                match self.dfg.value_data(value) {
+                    // If the value comes from the current block's parameter list, this use is trivially dominated
+                    ValueData::Param { block, .. } if block == &current_block => continue,
+                    // If the value comes from another block, then as long as all paths to the current
+                    // block flow through that block, then this use is dominated by its definition
+                    ValueData::Param { block, .. } => {
+                        if self.domtree.dominates(*block, current_block, &self.dfg) {
+                            continue;
+                        }
+                    }
+                    // If the value is an instruction result, then as long as all paths to the current
+                    // instruction flow through the defining instruction, then this use is dominated
+                    // by its definition
+                    ValueData::Inst { inst, .. } => {
+                        if self.domtree.dominates(*inst, node.key, &self.dfg) {
+                            continue;
+                        }
+                    }
+                }
+
+                // If we reach here, the use of `value` is not dominated by its definition,
+                // so this use is invalid
+                invalid_instruction!(
+                    diagnostics,
+                    node.key,
+                    span,
+                    "an argument of this instruction, {value}, is not defined on all paths leading to this point",
+                    "All uses of a value must be dominated by its definition, i.e. all control flow paths \
+                     from the function entry to the point of each use must flow through the point where \
+                     that value is defined."
+                );
+            }
+        }
+
+        Ok(())
+    }
+}
+
+/// This validation rule ensures that most block-local invariants are upheld:
+///
+/// * A block may not be empty
+/// * A block must end with a terminator instruction
+/// * A block may not contain a terminator instruction in any position but the end
+/// * A block which terminates with a branch instruction must reference a block
+///   that is present in the function body (i.e. it is not valid to reference
+///   detached blocks)
+/// * A multi-way branch instruction must have at least one successor
+/// * A multi-way branch instruction must not specify the same block as a successor multiple times.
+///
+/// This rule does not perform type checking, or verify use/def dominance.
+pub struct BlockValidator<'a> {
+    dfg: &'a DataFlowGraph,
+    span: SourceSpan,
+}
+impl<'a> BlockValidator<'a> {
+    pub fn new(dfg: &'a DataFlowGraph, span: SourceSpan) -> Self {
+        Self { dfg, span }
+    }
+}
+impl<'a> Rule<BlockData> for BlockValidator<'a> {
+    fn validate(
+        &mut self,
+        block_data: &BlockData,
+        diagnostics: &DiagnosticsHandler,
+    ) -> Result<(), ValidationError> {
+        // Ignore blocks which are not attached to the function body
+        if !block_data.link.is_linked() {
+            return Ok(());
+        }
+
+        // Ensure there is a terminator, and that it is valid
+        let id = block_data.id;
+        let terminator = block_data.insts.back().get();
+        if terminator.is_none() {
+            // This block is empty
+            invalid_block!(
+                diagnostics,
+                id,
+                self.span,
+                "block cannot be empty",
+                "Empty blocks are only valid when detached from the function body"
+            );
+        }
+
+        let terminator = terminator.unwrap();
+        let op = terminator.opcode();
+        if !op.is_terminator() {
+            invalid_block!(
+                diagnostics,
+                id,
+                self.span,
+                "invalid block terminator",
+                format!("The last instruction in a block must be a terminator, but {id} ends with {op} which is not a valid terminator")
+            );
+        }
+        match terminator.analyze_branch(&self.dfg.value_lists) {
+            BranchInfo::SingleDest(destination, _) => {
+                let dest = self.dfg.block(destination);
+                if !dest.link.is_linked() {
+                    invalid_instruction!(
+                        diagnostics,
+                        terminator.key,
+                        terminator.span(),
+                        "invalid successor",
+                        format!("A block reference is only valid if the referenced block is present in the function layout. \
+                                 {id} references {destination}, but the latter is not in the layout")
+                    );
+                }
+            }
+            BranchInfo::MultiDest(ref jts) => {
+                if jts.is_empty() {
+                    invalid_instruction!(
+                        diagnostics,
+                        terminator.key,
+                        terminator.span(),
+                        "incomplete {op} instruction",
+                        "This instruction normally has 2 or more successors, but none were given."
+                    );
+                }
+
+                let mut seen = SmallVec::<[Block; 4]>::default();
+                for jt in jts.iter() {
+                    let dest = self.dfg.block(jt.destination);
+                    let destination = jt.destination;
+                    if !dest.link.is_linked() {
+                        invalid_instruction!(
+                            diagnostics,
+                            terminator.key,
+                            terminator.span(),
+                            "invalid successor",
+                            format!("A block reference is only valid if the referenced block is present in the function layout. \
+                                    {id} references {destination}, but the latter is not in the layout")
+                        );
+                    }
+
+                    if seen.contains(&jt.destination) {
+                        invalid_instruction!(
+                            diagnostics,
+                            terminator.key,
+                            terminator.span(),
+                            "invalid {op} instruction",
+                            format!("A given block may only be a successor along a single control flow path, \
+                                     but {id} uses {destination} as a successor for more than one path")
+                        );
+                    }
+
+                    seen.push(jt.destination);
+                }
+            }
+            BranchInfo::NotABranch => (),
+        }
+
+        // Verify that there are no terminator instructions in any other position than last
+        for node in block_data.insts.iter() {
+            let op = node.opcode();
+            if op.is_terminator() && node.key != terminator.key {
+                invalid_block!(
+                    diagnostics,
+                    id,
+                    self.span,
+                    "terminator found in middle of block",
+                    format!("A block may only have a terminator instruction as the last instruction in the block, \
+                             but {id} uses {op} before the end of the block")
+                );
+            }
+        }
+
+        Ok(())
+    }
+}