Extended Description

Here is a transformation in test/Transform/LoopUnroll/pr45939-peel-count-and-complete-unroll.ll:

@​a = global [8 x i32] zeroinitializer, align 16

define void @​test1() {
; PEEL2-LABEL: @​test1(
; PEEL2-NEXT: entry:
; PEEL2-NEXT: br label [[FOR_BODY_PEEL_BEGIN:%.]]
; PEEL2: for.body.peel.begin:
; PEEL2-NEXT: br label [[FOR_BODY_PEEL:%.]]
; PEEL2: for.body.peel:
; PEEL2-NEXT: [[ARRAYIDX_PEEL:%.]] = getelementptr inbounds [8 x i32], [8 x i32] @​a, i64 0, i64 0
; PEEL2-NEXT: [[TMP0:%.]] = trunc i64 0 to i32
; PEEL2-NEXT: store i32 [[TMP0]], i32 [[ARRAYIDX_PEEL]], align 4
; PEEL2-NEXT: [[INDVARS_IV_NEXT_PEEL:%.]] = add nuw nsw i64 0, 1
; PEEL2-NEXT: [[EXITCOND_PEEL:%.]] = icmp ne i64 [[INDVARS_IV_NEXT_PEEL]], 8
; PEEL2-NEXT: br i1 [[EXITCOND_PEEL]], label [[FOR_BODY_PEEL_NEXT:%.]], label [[FOR_EXIT:%.]]
; PEEL2: for.body.peel.next:
; PEEL2-NEXT: br label [[FOR_BODY_PEEL2:%.]]
; PEEL2: for.body.peel2:
; PEEL2-NEXT: [[ARRAYIDX_PEEL3:%.]] = getelementptr inbounds [8 x i32], [8 x i32]* @​a, i64 0, i64 [[INDVARS_IV_NEXT_PEEL]]
; PEEL2-NEXT: [[TMP1:%.]] = trunc i64 [[INDVARS_IV_NEXT_PEEL]] to i32
; PEEL2-NEXT: store i32 [[TMP1]], i32 [[ARRAYIDX_PEEL3]], align 4
; PEEL2-NEXT: [[INDVARS_IV_NEXT_PEEL4:%.]] = add nuw nsw i64 [[INDVARS_IV_NEXT_PEEL]], 1
; PEEL2-NEXT: [[EXITCOND_PEEL5:%.]] = icmp ne i64 [[INDVARS_IV_NEXT_PEEL4]], 8
; PEEL2-NEXT: br i1 [[EXITCOND_PEEL5]], label [[FOR_BODY_PEEL_NEXT1:%.]], label [[FOR_EXIT]]
; PEEL2: for.body.peel.next1:
; PEEL2-NEXT: br label [[FOR_BODY_PEEL_NEXT6:%.]]
; PEEL2: for.body.peel.next6:
; PEEL2-NEXT: br label [[ENTRY_PEEL_NEWPH:%.]]
; PEEL2: entry.peel.newph:
; PEEL2-NEXT: br label [[FOR_BODY:%.]]
; PEEL2: for.body:
; PEEL2-NEXT: [[ARRAYIDX:%.]] = getelementptr inbounds [8 x i32], [8 x i32] @​a, i64 0, i64 [[INDVARS_IV_NEXT_PEEL4]]
; PEEL2-NEXT: [[TMP2:%.]] = trunc i64 [[INDVARS_IV_NEXT_PEEL4]] to i32
; PEEL2-NEXT: store i32 [[TMP2]], i32 [[ARRAYIDX]], align 4
; PEEL2-NEXT: store i32 3, i32* getelementptr inbounds ([8 x i32], [8 x i32]* @​a, i64 0, i64 3), align 4
; PEEL2-NEXT: store i32 4, i32* getelementptr inbounds ([8 x i32], [8 x i32]* @​a, i64 0, i64 4), align 4
; PEEL2-NEXT: store i32 5, i32* getelementptr inbounds ([8 x i32], [8 x i32]* @​a, i64 0, i64 5), align 4
; PEEL2-NEXT: store i32 6, i32* getelementptr inbounds ([8 x i32], [8 x i32]* @​a, i64 0, i64 6), align 4
; PEEL2-NEXT: store i32 7, i32* getelementptr inbounds ([8 x i32], [8 x i32]* @​a, i64 0, i64 7), align 4
; PEEL2-NEXT: store i32 8, i32* getelementptr inbounds ([8 x i32], [8 x i32]* @​a, i64 1, i64 0), align 4
; PEEL2-NEXT: store i32 9, i32* getelementptr ([8 x i32], [8 x i32]* @​a, i64 1, i64 1), align 4
; PEEL2-NEXT: br label [[FOR_EXIT]]
; PEEL2: for.exit:
; PEEL2-NEXT: ret void

entry:
br label %for.body

for.body: ; preds = %entry, %for.body
%indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
%arrayidx = getelementptr inbounds [8 x i32], [8 x i32]* @​a, i64 0, i64 %indvars.iv
%0 = trunc i64 %indvars.iv to i32
store i32 %0, i32* %arrayidx, align 4
%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
%exitcond = icmp ne i64 %indvars.iv.next, 8
br i1 %exitcond, label %for.body, label %for.exit

for.exit: ; preds = %for.body
ret void
}

The last two stores (store 8 and store 9) in transformed code writes to out-of-bounds addresses.