llvm(py): introduce BuildCtx + trace hub; refactor if-merge prepass + PHI wiring into module; unify logs; ctx-enable compare/ret/call/boxcall/externcall/typeop/newbox/safepoint; curated smoke option for if-merge; README updates; keep behavior stable

src/tests/mir_no_phi_merge_tests.rs

@@ -0,0 +1,62 @@
+use crate::ast::{ASTNode, LiteralValue, Span, BinaryOperator};
+use crate::mir::{MirCompiler, MirInstruction};
+
+fn lit_i(i: i64) -> ASTNode {
+    ASTNode::Literal { value: LiteralValue::Integer(i), span: Span::unknown() }
+}
+
+fn bool_lt(lhs: ASTNode, rhs: ASTNode) -> ASTNode {
+    ASTNode::BinaryOp { operator: BinaryOperator::LessThan, left: Box::new(lhs), right: Box::new(rhs), span: Span::unknown() }
+}
+
+#[test]
+fn mir13_no_phi_if_merge_inserts_edge_copies_for_return() {
+    // Force PHI-off mode
+    std::env::set_var("NYASH_MIR_NO_PHI", "1");
+
+    // if (1 < 2) { return 40 } else { return 50 }
+    let ast = ASTNode::If {
+        condition: Box::new(bool_lt(lit_i(1), lit_i(2))),
+        then_body: vec![ASTNode::Return { value: Some(Box::new(lit_i(40))), span: Span::unknown() }],
+        else_body: Some(vec![ASTNode::Return { value: Some(Box::new(lit_i(50))), span: Span::unknown() }]),
+        span: Span::unknown(),
+    };
+
+    let mut mc = MirCompiler::with_options(false);
+    let cr = mc.compile(ast).expect("compile");
+    let f = cr.module.functions.get("main").expect("function main");
+
+    // Find the block that returns a value and capture that return value id
+    let mut ret_block_id = None;
+    let mut ret_val = None;
+    for (bid, bb) in &f.blocks {
+        if let Some(MirInstruction::Return { value: Some(v) }) = bb.terminator.clone() {
+            ret_block_id = Some(*bid);
+            ret_val = Some(v);
+            break;
+        }
+    }
+    let ret_block = ret_block_id.expect("ret block");
+    let out_v = ret_val.expect("ret value");
+
+    // In PHI-off mode we expect copies into each predecessor of the merge/ret block
+    let preds: Vec<_> = f
+        .blocks
+        .get(&ret_block)
+        .expect("ret block present")
+        .predecessors
+        .iter()
+        .copied()
+        .collect();
+    assert!(preds.len() >= 2, "expected at least two predecessors at merge");
+
+    for p in preds {
+        let bb = f.blocks.get(&p).expect("pred block present");
+        let has_copy = bb
+            .instructions
+            .iter()
+            .any(|inst| matches!(inst, MirInstruction::Copy { dst, .. } if *dst == out_v));
+        assert!(has_copy, "expected Copy to out_v in predecessor {:?}", p);
+    }
+}
+