Fix nested loop unroll exit value repair

ir/function.cpp

@@ -608,10 +608,6 @@ void Function::unroll(unsigned k) {
   // computed bottom-up during the post-order traversal below
   unordered_map<BasicBlock*, vector<BasicBlock*>> loop_nodes;
 
-  // grab all value users before duplication so the list is shorter
-  auto users = getUsers();
-  auto phi_preds = getPhiPredecessors(*this);
-
   // traverse each loop tree in post-order
   while (!worklist.empty()) {
     auto [header, height, flag] = worklist.back();
@@ -644,6 +640,12 @@ void Function::unroll(unsigned k) {
       }
     }
 
+    // Grab value users before duplicating the current loop so the list stays
+    // shorter. This must be refreshed per loop because unrolling an inner loop
+    // can introduce phis that outer-loop exits now use.
+    auto users = getUsers();
+    auto phi_preds = getPhiPredecessors(*this);
+
     // map: original BB -> {BB} U copies-of-BB
     unordered_map<const BasicBlock*, vector<BasicBlock*>> bbmap;
     for (auto *bb : loop_bbs) {
@@ -1236,5 +1238,4 @@ void LoopAnalysis::printDot(ostream &os) const {
   os << "}\n";
 }
 
-} 
-
+}

tests/alive-tv/loops/nested-exit-phi.srctgt.ll

@@ -0,0 +1,27 @@
+; TEST-ARGS: -src-unroll=2 -tgt-unroll=2
+
+define i32 @src() {
+  br label %1
+
+1:
+  %2 = phi i32 [ 0, %0 ], [ 1, %6 ]
+  br label %3
+
+3:
+  %4 = mul i32 %2, 1
+  br label %5
+
+5:
+  br i1 false, label %3, label %6
+
+6:
+  %7 = icmp slt i32 %2, 1
+  br i1 %7, label %1, label %8
+
+8:
+  ret i32 %4
+}
+
+define i32 @tgt() {
+  ret i32 1
+}