From 811672be4ba81818a285fc371d95612505cdf000 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Motiejus=20Jak=C5=A1tys?= <motiejus@jakstys.lt>
Date: Fri, 13 Feb 2026 22:11:01 +0000
Subject: [PATCH] astgen: add isAlwaysVoid and endsWithNoReturn checks to
 rvalue

Port two missing checks from upstream AstGen.zig rvalueInner to the C
rvalue function:

1. isAlwaysVoid (Zir.zig:1343-1608): When the result refers to an
   instruction that always produces void (e.g., dbg_stmt, store_node,
   export, memcpy, etc.), replace the result with void_value before
   proceeding. This prevents emitting unnecessary type coercions or
   stores on always-void instructions.

2. endsWithNoReturn (AstGen.zig:11068): When the current GenZir block
   ends with a noreturn instruction, return the result immediately
   without emitting any rvalue instructions. This avoids emitting dead
   ZIR instructions after noreturn.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 astgen.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/astgen.c b/astgen.c
index 4342bd7a38..9206a2fed3 100644
--- a/astgen.c
+++ b/astgen.c
@@ -1906,9 +1906,72 @@ static uint32_t rlResultType(GenZir* gz, ResultLoc rl, uint32_t node) {
     }
 }
 
+static bool endsWithNoReturn(GenZir* gz);
+
+// Mirrors Zir.Inst.Tag.isAlwaysVoid (Zir.zig:1343-1608).
+static bool isAlwaysVoid(ZirInstTag tag, ZirInstData data) {
+    switch (tag) {
+    case ZIR_INST_DBG_STMT:
+    case ZIR_INST_DBG_VAR_PTR:
+    case ZIR_INST_DBG_VAR_VAL:
+    case ZIR_INST_ENSURE_RESULT_USED:
+    case ZIR_INST_ENSURE_RESULT_NON_ERROR:
+    case ZIR_INST_ENSURE_ERR_UNION_PAYLOAD_VOID:
+    case ZIR_INST_SET_EVAL_BRANCH_QUOTA:
+    case ZIR_INST_ATOMIC_STORE:
+    case ZIR_INST_STORE_NODE:
+    case ZIR_INST_STORE_TO_INFERRED_PTR:
+    case ZIR_INST_VALIDATE_DEREF:
+    case ZIR_INST_VALIDATE_DESTRUCTURE:
+    case ZIR_INST_EXPORT:
+    case ZIR_INST_SET_RUNTIME_SAFETY:
+    case ZIR_INST_MEMCPY:
+    case ZIR_INST_MEMSET:
+    case ZIR_INST_MEMMOVE:
+    case ZIR_INST_CHECK_COMPTIME_CONTROL_FLOW:
+    case ZIR_INST_DEFER:
+    case ZIR_INST_DEFER_ERR_CODE:
+    case ZIR_INST_SAVE_ERR_RET_INDEX:
+    case ZIR_INST_RESTORE_ERR_RET_INDEX_UNCONDITIONAL:
+    case ZIR_INST_RESTORE_ERR_RET_INDEX_FN_ENTRY:
+    case ZIR_INST_VALIDATE_STRUCT_INIT_TY:
+    case ZIR_INST_VALIDATE_STRUCT_INIT_RESULT_TY:
+    case ZIR_INST_VALIDATE_PTR_STRUCT_INIT:
+    case ZIR_INST_VALIDATE_ARRAY_INIT_TY:
+    case ZIR_INST_VALIDATE_ARRAY_INIT_RESULT_TY:
+    case ZIR_INST_VALIDATE_PTR_ARRAY_INIT:
+    case ZIR_INST_VALIDATE_REF_TY:
+    case ZIR_INST_VALIDATE_CONST:
+        return true;
+    case ZIR_INST_EXTENDED:
+        switch (data.extended.opcode) {
+        case ZIR_EXT_BRANCH_HINT:
+        case ZIR_EXT_BREAKPOINT:
+        case ZIR_EXT_DISABLE_INSTRUMENTATION:
+        case ZIR_EXT_DISABLE_INTRINSICS:
+            return true;
+        default:
+            return false;
+        }
+    default:
+        return false;
+    }
+}
+
 // rvalue (AstGen.zig:11051-11224): apply result location wrapping.
 static uint32_t rvalue(
     GenZir* gz, ResultLoc rl, uint32_t result, uint32_t node) {
+    // isAlwaysVoid check (AstGen.zig:11058-11067).
+    if (result >= ZIR_REF_START_INDEX) {
+        uint32_t result_index = result - ZIR_REF_START_INDEX;
+        if (isAlwaysVoid(gz->astgen->inst_tags[result_index],
+                gz->astgen->inst_datas[result_index])) {
+            result = ZIR_REF_VOID_VALUE;
+        }
+    }
+    // endsWithNoReturn check (AstGen.zig:11068).
+    if (endsWithNoReturn(gz))
+        return result;
     switch (rl.tag) {
     case RL_NONE:
     case RL_COERCED_TY: