From 0ea2b7d2cb74287232054f1b480cd03097f56810 Mon Sep 17 00:00:00 2001
From: nyash-codex <codex@nyash.local>
Date: Wed, 17 Dec 2025 16:12:16 +0900
Subject: [PATCH] fix(llvm_py): stabilize PHI incoming selection (no overwrite
 by failed candidate)

---
 .../current/main/phases/phase-97/README.md    |  1 +
 src/llvm_py/phi_wiring/wiring.py              | 38 +++++++++++++++++--
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/docs/development/current/main/phases/phase-97/README.md b/docs/development/current/main/phases/phase-97/README.md
index 953eeb6c..5a011c57 100644
--- a/docs/development/current/main/phases/phase-97/README.md
+++ b/docs/development/current/main/phases/phase-97/README.md
@@ -4,3 +4,4 @@
 - 新規 smoke: `phase97_next_non_ws_llvm_exe.sh`（apps/tests/phase96_json_loader_next_non_ws_min.hako）
   / `phase97_json_loader_escape_llvm_exe.sh`（apps/tests/phase95_json_loader_escape_min.hako）
 - LLVM/llvmlite が無い環境では SKIP（integration プロファイルのみで運用）
+- PHI wiring: duplicate incoming per pred の上書きバグを修正（0フォールバック回避）
diff --git a/src/llvm_py/phi_wiring/wiring.py b/src/llvm_py/phi_wiring/wiring.py
index a24ce11a..13cbe880 100644
--- a/src/llvm_py/phi_wiring/wiring.py
+++ b/src/llvm_py/phi_wiring/wiring.py
@@ -139,10 +139,24 @@ def nearest_pred_on_path(
 
 def wire_incomings(builder, block_id: int, dst_vid: int, incoming: List[Tuple[int, int]], context=None):
     """Wire PHI incoming edges for (block_id, dst_vid) using declared (decl_b, v_src) pairs.
+
     Phase 132-P1: Use context Box for function-local state isolation.
 
-    Args:
-        context: FunctionLowerContext Box containing function-local state
+    SSOT: duplicate incoming per predecessor
+    ----------------------------------------
+    LLVM PHI wiring may observe *multiple* incoming candidates that map to the same actual
+    predecessor (`pred_match`). This can happen legitimately because:
+    - jump-only / trampoline blocks: multiple declared blocks collapse to the same CFG predecessor,
+    - alias/self-carry handling: placeholder `dst_vid` appears in the incoming list and is rewritten,
+    - prepass placeholders: additional metadata can create redundant candidates.
+
+    Selection contract:
+    - Once a predecessor’s incoming value is successfully chosen, do not overwrite it later
+      (avoid last-wins instability).
+    - A synthesized `0` is treated as an "unresolved sentinel" (fallback path). If we later obtain
+      a successfully-resolved non-zero value for the same predecessor, we may replace `0`.
+    - In STRICT mode, `0` should be rare; a `0` incoming indicates "missing snapshot / unresolved"
+      and should be caught by stricter checks upstream.
     """
     bb = builder.bb_map.get(block_id)
     if bb is None:
@@ -201,6 +215,15 @@ def wire_incomings(builder, block_id: int, dst_vid: int, incoming: List[Tuple[in
             init_src_vid = vi
             break
     chosen: Dict[int, ir.Value] = {}
+
+    def _is_zero_const(v: ir.Value) -> bool:
+        try:
+            if isinstance(v, ir.Constant) and isinstance(v.type, ir.IntType) and v.type.width == 64:
+                return int(getattr(v, "constant", 1)) == 0
+        except Exception:
+            pass
+        return False
+
     for (b_decl, v_src) in incoming:
         try:
             bd = int(b_decl)
@@ -227,6 +250,7 @@ def wire_incomings(builder, block_id: int, dst_vid: int, incoming: List[Tuple[in
         except Exception as e:
             trace({"phi": "wire_resolve_fail", "vs": vs, "pred": pred_match, "error": str(e)})
             val = None
+        resolved_ok = val is not None
         # Normalize to a well-typed LLVM value (i64)
         if val is None:
             val = _const_i64(builder, 0)
@@ -237,7 +261,15 @@ def wire_incomings(builder, block_id: int, dst_vid: int, incoming: List[Tuple[in
                     val = _const_i64(builder, int(val))
             except Exception:
                 val = _const_i64(builder, 0)
-        chosen[pred_match] = val
+        # SSOT for ambiguous PHI incoming (same pred_match multiple times):
+        # - prefer a non-zero / successfully-resolved value over a synthesized zero,
+        # - otherwise keep the first choice to avoid last-wins "overwrite to 0".
+        prev = chosen.get(pred_match)
+        if prev is None:
+            chosen[pred_match] = val
+        else:
+            if _is_zero_const(prev) and not _is_zero_const(val) and resolved_ok:
+                chosen[pred_match] = val
         trace({"phi": "wire_choose", "pred": int(pred_match), "dst": int(dst_vid), "src": int(vs)})
     wired = 0
     for pred_bid, val in chosen.items():