fix: Add a remove_unreachable_instructions SSA pass (zeroing out terminators)

compiler/noirc_evaluator/src/ssa.rs

@@ -138,6 +138,7 @@ pub struct ArtifactsAndWarnings(pub Artifacts, pub Vec<SsaReport>);
 /// something we take can advantage of in the [secondary_passes].
 pub fn primary_passes(options: &SsaEvaluatorOptions) -> Vec<SsaPass> {
     vec![
+        SsaPass::new(Ssa::remove_unreachable_instructions, "Remove Unreachable Instructions"),
         SsaPass::new(Ssa::remove_unreachable_functions, "Removing Unreachable Functions"),
         SsaPass::new(Ssa::defunctionalize, "Defunctionalization"),
         SsaPass::new(Ssa::inline_simple_functions, "Inlining simple functions"),
@@ -213,7 +214,9 @@ pub fn primary_passes(options: &SsaEvaluatorOptions) -> Vec<SsaPass> {
         SsaPass::new(Ssa::brillig_array_get_and_set, "Brillig Array Get and Set Optimizations"),
         // Perform another DIE pass to update the used globals after offsetting Brillig indexes.
         SsaPass::new(Ssa::dead_instruction_elimination, "Dead Instruction Elimination"),
-        // A function can be potentially unreachable post-DIE if all calls to that function were removed.
+        SsaPass::new(Ssa::remove_unreachable_instructions, "Remove Unreachable Instructions"),
+        // A function can be potentially unreachable post-DIE if all calls to that function were removed,
+        // or after the removal of unreachable instructions.
         SsaPass::new(Ssa::remove_unreachable_functions, "Removing Unreachable Functions"),
         SsaPass::new(Ssa::checked_to_unchecked, "Checked to unchecked"),
         SsaPass::new_try(
@@ -229,6 +232,7 @@ pub fn primary_passes(options: &SsaEvaluatorOptions) -> Vec<SsaPass> {
 pub fn secondary_passes(brillig: &Brillig) -> Vec<SsaPass> {
     vec![
         SsaPass::new(move |ssa| ssa.fold_constants_with_brillig(brillig), "Inlining Brillig Calls"),
+        SsaPass::new(Ssa::remove_unreachable_instructions, "Remove Unreachable Instructions"),
         // It could happen that we inlined all calls to a given brillig function.
         // In that case it's unused so we can remove it. This is what we check next.
         SsaPass::new(Ssa::remove_unreachable_functions, "Removing Unreachable Functions"),

compiler/noirc_evaluator/src/ssa/opt/mod.rs

@@ -31,6 +31,7 @@ mod remove_enable_side_effects;
 mod remove_if_else;
 mod remove_truncate_after_range_check;
 mod remove_unreachable;
+mod remove_unreachable_instructions;
 mod simple_optimization;
 mod simplify_cfg;
 mod unrolling;