phase29ao(p13): block_params for pattern3 if-phi merge join

src/mir/builder/control_flow/plan/normalizer/pattern3_if_phi.rs

@@ -1,7 +1,7 @@
 use super::helpers::{create_phi_bindings, LoopBlocksWithIfPhi};
 use super::{CoreEffectPlan, CoreLoopPlan, CorePhiInfo, CorePlan, Pattern3IfPhiPlan};
 use crate::mir::basic_block::EdgeArgs;
-use crate::mir::builder::control_flow::edgecfg::api::{BranchStub, EdgeStub, ExitKind, Frag};
+use crate::mir::builder::control_flow::edgecfg::api::{BlockParams, BranchStub, EdgeStub, ExitKind, Frag};
 use crate::mir::builder::control_flow::joinir::patterns::router::LoopPatternContext;
 use crate::mir::builder::MirBuilder;
 use crate::mir::join_ir::lowering::inline_boundary::JumpArgsLayout;
@@ -13,7 +13,8 @@ impl super::PlanNormalizer {
     ///
     /// Expands Pattern3 (Loop with If-Phi) semantics into generic CorePlan:
     /// - CFG structure: preheader → header → body → then/else → merge → step → header
-    /// - 3 PHIs: 2 in header (loop_var, carrier), 1 in merge (carrier_next)
+    /// - 2 PHIs: in header (loop_var, carrier)
+    /// - merge join (carrier_next) is expressed via `Frag.block_params + EdgeArgs`
     /// - If-else branching with PHI merge (no Select instruction)
     pub(super) fn normalize_pattern3_if_phi(
         builder: &mut MirBuilder,
@@ -171,7 +172,7 @@ impl super::PlanNormalizer {
             (step_bb, step_effects),
         ];
 
-        // Step 13: Build PHIs
+        // Step 13: Build PHIs (2 PHIs in header only)
         let phis = vec![
             CorePhiInfo {
                 block: header_bb,
@@ -185,20 +186,23 @@ impl super::PlanNormalizer {
                 inputs: vec![(preheader_bb, carrier_init), (step_bb, carrier_next)],
                 tag: format!("carrier_{}", parts.carrier_var),
             },
-            CorePhiInfo {
-                block: merge_bb,
-                dst: carrier_next,
-                inputs: vec![(then_bb, carrier_then), (else_bb, carrier_else)],
-                tag: format!("merge_{}", parts.carrier_var),
-            },
         ];
 
-        // Step 14: Build Frag
+        // Step 14: Build Frag (merge join via block_params + edge args)
         let empty_args = EdgeArgs {
             layout: JumpArgsLayout::CarriersOnly,
             values: vec![],
         };
 
+        let merge_join_args_then = EdgeArgs {
+            layout: JumpArgsLayout::ExprResultPlusCarriers,
+            values: vec![carrier_then],
+        };
+        let merge_join_args_else = EdgeArgs {
+            layout: JumpArgsLayout::ExprResultPlusCarriers,
+            values: vec![carrier_else],
+        };
+
         let branches = vec![
             BranchStub {
                 from: header_bb,
@@ -223,13 +227,13 @@ impl super::PlanNormalizer {
                 from: then_bb,
                 kind: ExitKind::Normal,
                 target: Some(merge_bb),
-                args: empty_args.clone(),
+                args: merge_join_args_then,
             },
             EdgeStub {
                 from: else_bb,
                 kind: ExitKind::Normal,
                 target: Some(merge_bb),
-                args: empty_args.clone(),
+                args: merge_join_args_else,
             },
             EdgeStub {
                 from: merge_bb,
@@ -245,9 +249,18 @@ impl super::PlanNormalizer {
             },
         ];
 
+        let mut block_params = BTreeMap::new();
+        block_params.insert(
+            merge_bb,
+            BlockParams {
+                layout: JumpArgsLayout::ExprResultPlusCarriers,
+                params: vec![carrier_next],
+            },
+        );
+
         let frag = Frag {
             entry: header_bb,
-            block_params: BTreeMap::new(),
+            block_params,
             exits: BTreeMap::new(),
             wires,
             branches,
@@ -279,7 +292,7 @@ impl super::PlanNormalizer {
         if debug {
             trace_logger.debug(
                 "normalizer/pattern3_if_phi",
-                "CorePlan construction complete (7 blocks, 3 PHIs)",
+                "CorePlan construction complete (7 blocks, 2 PHIs + merge join via block_params)",
             );
         }