[LSR] Clear SCEVExpander before deleting phi nodes

Fixes llvm#84709.

Author: nikic

llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -6971,6 +6971,7 @@ static bool ReduceLoopStrength(Loop *L, IVUsers &IU, ScalarEvolution &SE,
     Rewriter.setDebugType(DEBUG_TYPE);
 #endif
     unsigned numFolded = Rewriter.replaceCongruentIVs(L, &DT, DeadInsts, &TTI);
+    Rewriter.clear();
     if (numFolded) {
       Changed = true;
       RecursivelyDeleteTriviallyDeadInstructionsPermissive(DeadInsts, &TLI,
@@ -6989,6 +6990,7 @@ static bool ReduceLoopStrength(Loop *L, IVUsers &IU, ScalarEvolution &SE,
     SCEVExpander Rewriter(SE, DL, "lsr", true);
     int Rewrites = rewriteLoopExitValues(L, &LI, &TLI, &SE, &TTI, Rewriter, &DT,
                                          UnusedIndVarInLoop, DeadInsts);
+    Rewriter.clear();
     if (Rewrites) {
       Changed = true;
       RecursivelyDeleteTriviallyDeadInstructionsPermissive(DeadInsts, &TLI,

llvm/test/Transforms/LoopStrengthReduce/pr84709.ll

@@ -0,0 +1,34 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -S -passes=loop-reduce < %s | FileCheck %s
+
+; Make sure it does not assert.
+define i64 @test() {
+; CHECK-LABEL: define i64 @test() {
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    br label [[BB2:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    br i1 true, label [[BB5:%.*]], label [[BB2]]
+; CHECK:       bb5:
+; CHECK-NEXT:    br label [[BB1]]
+;
+bb:
+  br label %bb1
+
+bb1:
+  %phi = phi i8 [ %zext6, %bb5 ], [ 0, %bb ]
+  br label %bb2
+
+bb2:
+  %phi3 = phi i8 [ %add, %bb2 ], [ %phi, %bb1 ]
+  %phi4 = phi i32 [ 0, %bb2 ], [ 1, %bb1 ]
+  %add = add i8 %phi3, 1
+  br i1 true, label %bb5, label %bb2
+
+bb5:
+  %zext = zext i8 %add to i32
+  %icmp = icmp sge i32 %phi4, 0
+  %zext6 = zext i1 %icmp to i8
+  br label %bb1
+}