[LSR] Clear SCEVExpander before calling DeleteDeadPHIs

To avoid an assertion failure when an AssertingVH is removed,
as reported in:
#82362 (comment)

Also remove an unnecessary use of SCEVExpanderCleaner.

llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -7033,7 +7033,6 @@ static bool ReduceLoopStrength(Loop *L, IVUsers &IU, ScalarEvolution &SE,
       // SCEVExpander for both use in preheader and latch
       const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
       SCEVExpander Expander(SE, DL, "lsr_fold_term_cond");
-      SCEVExpanderCleaner ExpCleaner(Expander);
 
       assert(Expander.isSafeToExpand(TermValueS) &&
              "Terminating value was checked safe in canFoldTerminatingCondition");
@@ -7064,10 +7063,9 @@ static bool ReduceLoopStrength(Loop *L, IVUsers &IU, ScalarEvolution &SE,
 
       BI->setCondition(NewTermCond);
 
+      Expander.clear();
       OldTermCond->eraseFromParent();
       DeleteDeadPHIs(L->getHeader(), &TLI, MSSAU.get());
-
-      ExpCleaner.markResultUsed();
     }
   }
 

llvm/test/Transforms/LoopStrengthReduce/RISCV/term-fold-crash.ll

@@ -0,0 +1,43 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -S -passes=loop-reduce -mtriple=riscv64-unknown-linux-gnu < %s | FileCheck %s
+
+define void @test(ptr %p, i8 %arg, i32 %start) {
+; CHECK-LABEL: define void @test(
+; CHECK-SAME: ptr [[P:%.*]], i8 [[ARG:%.*]], i32 [[START:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CONV:%.*]] = zext i8 [[ARG]] to i32
+; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[CONV]], 1
+; CHECK-NEXT:    [[TMP0:%.*]] = add i32 [[START]], [[SHR]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i32 [[TMP0]], 1
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[ADD810:%.*]] = phi i32 [ [[START]], [[ENTRY:%.*]] ], [ [[ADD:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[IDXPROM2:%.*]] = zext i32 [[ADD810]] to i64
+; CHECK-NEXT:    [[ARRAYIDX3:%.*]] = getelementptr i8, ptr [[P]], i64 [[IDXPROM2]]
+; CHECK-NEXT:    [[V:%.*]] = load i8, ptr [[ARRAYIDX3]], align 1
+; CHECK-NEXT:    [[ADD]] = add i32 [[ADD810]], 1
+; CHECK-NEXT:    [[LSR_FOLD_TERM_COND_REPLACED_TERM_COND:%.*]] = icmp eq i32 [[ADD]], [[TMP1]]
+; CHECK-NEXT:    br i1 [[LSR_FOLD_TERM_COND_REPLACED_TERM_COND]], label [[EXIT:%.*]], label [[FOR_BODY]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %conv = zext i8 %arg to i32
+  %shr = lshr i32 %conv, 1
+  %wide.trip.count = zext nneg i32 %shr to i64
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %add810 = phi i32 [ %start, %entry ], [ %add, %for.body ]
+  %idxprom2 = zext i32 %add810 to i64
+  %arrayidx3 = getelementptr i8, ptr %p, i64 %idxprom2
+  %v = load i8, ptr %arrayidx3, align 1
+  %add = add i32 %add810, 1
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv, %wide.trip.count
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  ret void
+}