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llvm-project/llvm/test/Transforms/LoopDeletion/pr53969.ll
Max Kazantsev ad3b1fe472 [SCEV] Do not erase LoopUsers. PR53969 
This patch fixes a logical error in how we work with `LoopUsers` map.
It maps a loop onto a set of AddRecs that depend on it. The Addrecs
are added to this map only once when they are created and put to
the UniqueSCEVs` map.

The only purpose of this map is to make sure that, whenever we forget
a loop, all (directly or indirectly) dependent SCEVs get forgotten too.

Current code erases SCEVs from dependent set of a given loop whenever
we forget this loop. This is not a correct behavior due to the following scenario:

1. We have a loop `L` and an AddRec `AR` that depends on it;
2. We modify something in the loop, but don't destroy it. We still call forgetLoop on it;
3. `AR` is no longer dependent on `L` according to `LoopUsers`. It is erased from
    ValueExprMap` and `ExprValue map, but still exists in UniqueSCEVs;
4. We can later request the very same AddRec for the very same loop again, and get existing
    SCEV `AR`.
5. Now, `AR` exists and is used again, but its notion that it depends on `L` is lost;
6. Then we decide to delete `L`. `AR` will not be forgotten because we have lost it;
7. Just you wait when you run into a dangling pointer problem, or any other kind of problem
   because an active SCEV is now referecing a non-existent loop.

The solution to this is to stop erasing values from `LoopUsers`. Yes, we will maybe forget something
that is already not used, but it's cheap.

This fixes a functional bug and potentially may have negative compile time impact on methods with
huge or numerous loops.

Differential Revision: https://reviews.llvm.org/D120303
Reviewed By: nikic
2022-02-22 17:24:39 +07:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -passes="loop(indvars,loop-deletion)" -S < %s | FileCheck %s
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128-ni:1-p2:32:8:8:32-ni:2"
target triple = "x86_64-unknown-linux-gnu"
; Make sure we don't crash.
define void @test() {
; CHECK-LABEL: @test(
; CHECK-NEXT: bb:
; CHECK-NEXT: br label [[BB1:%.*]]
; CHECK: bb1:
; CHECK-NEXT: [[TMP2:%.*]] = phi i32 [ 11, [[BB:%.*]] ]
; CHECK-NEXT: [[TMP3:%.*]] = add nsw i32 112, -1
; CHECK-NEXT: [[TMP4:%.*]] = add nuw nsw i32 [[TMP2]], 1
; CHECK-NEXT: [[TMP5:%.*]] = mul i32 [[TMP3]], [[TMP3]]
; CHECK-NEXT: [[TMP6:%.*]] = mul nsw i32 [[TMP2]], -6
; CHECK-NEXT: [[TMP7:%.*]] = mul nsw i32 [[TMP6]], [[TMP5]]
; CHECK-NEXT: [[TMP8:%.*]] = add nuw nsw i32 [[TMP7]], [[TMP2]]
; CHECK-NEXT: [[TMP9:%.*]] = and i32 undef, 1
; CHECK-NEXT: [[TMP10:%.*]] = icmp eq i32 [[TMP9]], 0
; CHECK-NEXT: br i1 [[TMP10]], label [[BB33_LOOPEXIT1:%.*]], label [[BB34_PREHEADER:%.*]]
; CHECK: bb34.preheader:
; CHECK-NEXT: br label [[BB34:%.*]]
; CHECK: bb11:
; CHECK-NEXT: [[TMP2_LCSSA12:%.*]] = phi i32 [ 11, [[BB34]] ]
; CHECK-NEXT: br label [[BB33_LOOPEXIT:%.*]]
; CHECK: bb12:
; CHECK-NEXT: [[TMP0:%.*]] = add i64 [[TMP40:%.*]], 0
; CHECK-NEXT: br label [[BB14:%.*]]
; CHECK: bb14:
; CHECK-NEXT: br i1 true, label [[BB32:%.*]], label [[BB22:%.*]]
; CHECK: bb22:
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 4 to i32
; CHECK-NEXT: [[TMP23:%.*]] = or i32 [[TMP1]], undef
; CHECK-NEXT: [[TMP24:%.*]] = add i32 [[TMP23]], undef
; CHECK-NEXT: br i1 false, label [[BB42:%.*]], label [[BB25:%.*]]
; CHECK: bb25:
; CHECK-NEXT: br label [[BB31:%.*]]
; CHECK: bb31:
; CHECK-NEXT: unreachable
; CHECK: bb32:
; CHECK-NEXT: ret void
; CHECK: bb33.loopexit:
; CHECK-NEXT: [[TMP2_LCSSA9:%.*]] = phi i32 [ [[TMP2_LCSSA12]], [[BB11:%.*]] ]
; CHECK-NEXT: br label [[BB33:%.*]]
; CHECK: bb33.loopexit1:
; CHECK-NEXT: [[TMP2_LCSSA:%.*]] = phi i32 [ [[TMP2]], [[BB1]] ]
; CHECK-NEXT: br label [[BB33]]
; CHECK: bb33:
; CHECK-NEXT: [[TMP210:%.*]] = phi i32 [ [[TMP2_LCSSA]], [[BB33_LOOPEXIT1]] ], [ [[TMP2_LCSSA9]], [[BB33_LOOPEXIT]] ]
; CHECK-NEXT: call void @use(i32 [[TMP210]])
; CHECK-NEXT: ret void
; CHECK: bb34:
; CHECK-NEXT: [[TMP36:%.*]] = xor i32 0, [[TMP8]]
; CHECK-NEXT: [[TMP38:%.*]] = add i32 [[TMP36]], undef
; CHECK-NEXT: [[TMP39:%.*]] = add i32 [[TMP38]], undef
; CHECK-NEXT: [[TMP40]] = sext i32 [[TMP39]] to i64
; CHECK-NEXT: br i1 false, label [[BB11]], label [[BB12:%.*]]
; CHECK: bb42:
; CHECK-NEXT: [[TMP24_LCSSA:%.*]] = phi i32 [ [[TMP24]], [[BB22]] ]
; CHECK-NEXT: [[TMP18_LCSSA4:%.*]] = phi i64 [ [[TMP0]], [[BB22]] ]
; CHECK-NEXT: store atomic i64 [[TMP18_LCSSA4]], i64 addrspace(1)* undef unordered, align 8
; CHECK-NEXT: call void @use(i32 [[TMP24_LCSSA]])
; CHECK-NEXT: ret void
;
bb:
br label %bb1
bb1: ; preds = %bb31, %bb
%tmp = phi i32 [ %tmp29, %bb31 ], [ undef, %bb ]
%tmp2 = phi i32 [ %tmp4, %bb31 ], [ 11, %bb ]
%tmp3 = add nsw i32 112, -1
%tmp4 = add nuw nsw i32 %tmp2, 1
%tmp5 = mul i32 %tmp3, %tmp3
%tmp6 = mul nsw i32 %tmp2, -6
%tmp7 = mul i32 %tmp6, %tmp5
%tmp8 = add i32 %tmp7, %tmp2
%tmp9 = and i32 undef, 1
%tmp10 = icmp eq i32 %tmp9, 0
br i1 %tmp10, label %bb33, label %bb34
bb11: ; preds = %bb34
br i1 undef, label %bb33, label %bb34
bb12: ; preds = %bb34
%tmp13 = icmp eq i8 addrspace(1)* undef, null
br label %bb14
bb14: ; preds = %bb25, %bb12
%tmp15 = phi i32 [ %tmp29, %bb25 ], [ %tmp37, %bb12 ]
%tmp16 = phi i64 [ undef, %bb25 ], [ %tmp41, %bb12 ]
%tmp17 = phi i32 [ %tmp26, %bb25 ], [ 4, %bb12 ]
%tmp18 = add i64 %tmp16, undef
%tmp19 = add i32 %tmp15, 1
%tmp20 = and i32 %tmp19, 1
%tmp21 = icmp eq i32 %tmp20, 0
br i1 %tmp21, label %bb32, label %bb22
bb22: ; preds = %bb14
%tmp23 = or i32 %tmp17, undef
%tmp24 = add i32 %tmp23, undef
br i1 %tmp13, label %bb42, label %bb25
bb25: ; preds = %bb22
%tmp26 = add nuw nsw i32 %tmp17, 1
%tmp27 = zext i32 %tmp26 to i64
%tmp28 = getelementptr inbounds i32, i32 addrspace(1)* undef, i64 %tmp27
%tmp29 = add i32 %tmp15, 3
%tmp30 = icmp ugt i32 %tmp17, 110
br i1 %tmp30, label %bb31, label %bb14
bb31: ; preds = %bb25
br label %bb1
bb32: ; preds = %bb14
ret void
bb33: ; preds = %bb11, %bb1
call void @use(i32 %tmp2)
ret void
bb34: ; preds = %bb11, %bb1
%tmp35 = phi i32 [ %tmp37, %bb11 ], [ %tmp, %bb1 ]
%tmp36 = xor i32 0, %tmp8
%tmp37 = add i32 %tmp35, 2
%tmp38 = add i32 %tmp36, undef
%tmp39 = add i32 %tmp38, undef
%tmp40 = sext i32 %tmp39 to i64
%tmp41 = add i64 undef, %tmp40
br i1 undef, label %bb11, label %bb12
bb42: ; preds = %bb22
store atomic i64 %tmp18, i64 addrspace(1)* undef unordered, align 8
call void @use(i32 %tmp24)
ret void
}
declare void @use(i32)
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