diff --git a/src/mir/basic_block.rs b/src/mir/basic_block.rs
index 88953c72..7db19dbf 100644
--- a/src/mir/basic_block.rs
+++ b/src/mir/basic_block.rs
@@ -5,7 +5,7 @@
  */
 
 use super::{EffectMask, MirInstruction, ValueId};
-use std::collections::HashSet;
+use std::collections::{HashMap, HashSet};
 use std::fmt;
 
 /// Unique identifier for basic blocks within a function
@@ -219,6 +219,24 @@ impl BasicBlock {
         self.instructions.insert(phi_count, instruction);
     }
 
+    /// Update PHI instruction input by destination ValueId
+    /// Used for loop back-edge PHI updates
+    pub fn update_phi_input(
+        &mut self,
+        phi_dst: ValueId,
+        incoming: (BasicBlockId, ValueId),
+    ) -> Result<(), String> {
+        for inst in &mut self.instructions {
+            if let MirInstruction::Phi { dst, inputs } = inst {
+                if *dst == phi_dst {
+                    inputs.push(incoming);
+                    return Ok(());
+                }
+            }
+        }
+        Err(format!("PHI instruction with dst {:?} not found in block {:?}", phi_dst, self.id))
+    }
+
     /// Replace terminator instruction
     pub fn set_terminator(&mut self, terminator: MirInstruction) {
         if !self.is_terminator(&terminator) {
diff --git a/src/mir/function.rs b/src/mir/function.rs
index 5351f341..3cb79a05 100644
--- a/src/mir/function.rs
+++ b/src/mir/function.rs
@@ -4,7 +4,7 @@
  * Functions contain basic blocks and SSA values, modules contain functions
  */
 
-use super::{BasicBlock, BasicBlockId, EffectMask, MirType, ValueId};
+use super::{BasicBlock, BasicBlockId, EffectMask, MirInstruction, MirType, ValueId};
 use std::collections::HashMap;
 use std::fmt;
 
@@ -249,6 +249,44 @@ impl MirFunction {
             is_pure: self.signature.effects.is_pure(),
         }
     }
+
+    /// Set jump terminator if block is not already terminated
+    /// Helper for JSON v0 Bridge and loop lowering
+    pub fn set_jump_terminator(
+        &mut self,
+        bb_id: BasicBlockId,
+        target: BasicBlockId,
+    ) -> Result<(), String> {
+        if let Some(bb) = self.get_block_mut(bb_id) {
+            if !bb.is_terminated() {
+                bb.set_terminator(MirInstruction::Jump { target });
+            }
+            Ok(())
+        } else {
+            Err(format!("Block {:?} not found", bb_id))
+        }
+    }
+
+    /// Set branch terminator
+    /// Helper for JSON v0 Bridge if/else lowering
+    pub fn set_branch_terminator(
+        &mut self,
+        bb_id: BasicBlockId,
+        condition: ValueId,
+        then_bb: BasicBlockId,
+        else_bb: BasicBlockId,
+    ) -> Result<(), String> {
+        if let Some(bb) = self.get_block_mut(bb_id) {
+            bb.set_terminator(MirInstruction::Branch {
+                condition,
+                then_bb,
+                else_bb,
+            });
+            Ok(())
+        } else {
+            Err(format!("Block {:?} not found", bb_id))
+        }
+    }
 }
 
 /// Function statistics for profiling and optimization