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[LoopPeel] Turn incorrect assert into a check
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Summary:
This patch replaces incorrectt assert with a check. Previously it asserts that
if SCEV cannot prove `isKnownPredicate(A != B)`, then it should be able to prove
`isKnownPredicate(A == B)`.

Both these fact may be not provable. It is shown in the provided test:

Could not prove: `{-294,+,-2}<%bb1> !=  0`
Asserting: `{-294,+,-2}<%bb1> == 0`

Obviously, this SCEV is not equal to zero, but 0 is in its range so we cannot
also prove that it is not zero.

Instead of assert, we should be checking the required conditions explicitly.

Reviewers: lebedev.ri, fhahn, sanjoy, fedor.sergeev
Reviewed By: lebedev.ri
Subscribers: hiraditya, zzheng, javed.absar, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76050
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Max Kazantsev authored and Fedor Sergeev committed Mar 12, 2020
1 parent b720543 commit 3dc6e53
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Showing 2 changed files with 113 additions and 4 deletions.
7 changes: 3 additions & 4 deletions llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp
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Expand Up @@ -262,10 +262,9 @@ static unsigned countToEliminateCompares(Loop &L, unsigned MaxPeelCount,
// iteration. See if that makes !Pred become unknown again.
if (ICmpInst::isEquality(Pred) &&
!SE.isKnownPredicate(ICmpInst::getInversePredicate(Pred), NextIterVal,
RightSCEV)) {
assert(!SE.isKnownPredicate(Pred, IterVal, RightSCEV) &&
SE.isKnownPredicate(Pred, NextIterVal, RightSCEV) &&
"Expected Pred to go from known to unknown.");
RightSCEV) &&
!SE.isKnownPredicate(Pred, IterVal, RightSCEV) &&
SE.isKnownPredicate(Pred, NextIterVal, RightSCEV)) {
if (!CanPeelOneMoreIteration())
continue; // Need to peel one more iteration, but can't. Give up.
PeelOneMoreIteration(); // Great!
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110 changes: 110 additions & 0 deletions llvm/test/Transforms/LoopUnroll/wrong_assert_in_peeling.ll
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@@ -0,0 +1,110 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S < %s -loop-unroll | FileCheck %s
; RUN: opt -S < %s -passes=unroll | 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"

define i32 @test() {
; CHECK-LABEL: @test(
; CHECK-NEXT: bb:
; CHECK-NEXT: br label [[BB1:%.*]]
; CHECK: bb1:
; CHECK-NEXT: [[TMP:%.*]] = phi i32 [ -147, [[BB:%.*]] ], [ [[TMP14:%.*]], [[BB13:%.*]] ]
; CHECK-NEXT: br label [[BB2_PEEL_BEGIN:%.*]]
; CHECK: bb2.peel.begin:
; CHECK-NEXT: br label [[BB2_PEEL:%.*]]
; CHECK: bb2.peel:
; CHECK-NEXT: [[TMP4_PEEL:%.*]] = add nsw i32 undef, [[TMP]]
; CHECK-NEXT: br label [[BB5_PEEL:%.*]]
; CHECK: bb5.peel:
; CHECK-NEXT: [[TMP6_PEEL:%.*]] = icmp eq i32 undef, 33
; CHECK-NEXT: br i1 [[TMP6_PEEL]], label [[BB7_PEEL:%.*]], label [[BB15_LOOPEXIT2:%.*]]
; CHECK: bb7.peel:
; CHECK-NEXT: [[TMP8_PEEL:%.*]] = sub nsw i32 undef, undef
; CHECK-NEXT: [[TMP9_PEEL:%.*]] = icmp eq i32 [[TMP8_PEEL]], 0
; CHECK-NEXT: br i1 [[TMP9_PEEL]], label [[BB10_PEEL:%.*]], label [[BB10_PEEL]]
; CHECK: bb10.peel:
; CHECK-NEXT: [[TMP11_PEEL:%.*]] = icmp eq i8 undef, 0
; CHECK-NEXT: br i1 [[TMP11_PEEL]], label [[BB12_PEEL:%.*]], label [[BB17_LOOPEXIT3:%.*]]
; CHECK: bb12.peel:
; CHECK-NEXT: br i1 false, label [[BB13]], label [[BB2_PEEL_NEXT:%.*]]
; CHECK: bb2.peel.next:
; CHECK-NEXT: br label [[BB2_PEEL_NEXT1:%.*]]
; CHECK: bb2.peel.next1:
; CHECK-NEXT: br label [[BB1_PEEL_NEWPH:%.*]]
; CHECK: bb1.peel.newph:
; CHECK-NEXT: br label [[BB2:%.*]]
; CHECK: bb2:
; CHECK-NEXT: [[TMP3:%.*]] = phi i32 [ [[TMP4_PEEL]], [[BB1_PEEL_NEWPH]] ], [ [[TMP4:%.*]], [[BB12:%.*]] ]
; CHECK-NEXT: [[TMP4]] = add nsw i32 [[TMP3]], [[TMP]]
; CHECK-NEXT: br label [[BB5:%.*]]
; CHECK: bb5:
; CHECK-NEXT: br i1 false, label [[BB7:%.*]], label [[BB15_LOOPEXIT:%.*]]
; CHECK: bb7:
; CHECK-NEXT: br i1 undef, label [[BB10:%.*]], label [[BB10]]
; CHECK: bb10:
; CHECK-NEXT: br i1 false, label [[BB12]], label [[BB17_LOOPEXIT:%.*]]
; CHECK: bb12:
; CHECK-NEXT: br i1 false, label [[BB13_LOOPEXIT:%.*]], label [[BB2]], !llvm.loop !0
; CHECK: bb13.loopexit:
; CHECK-NEXT: br label [[BB13]]
; CHECK: bb13:
; CHECK-NEXT: [[TMP14]] = add nsw i32 [[TMP]], -1
; CHECK-NEXT: br label [[BB1]]
; CHECK: bb15.loopexit:
; CHECK-NEXT: br label [[BB15:%.*]]
; CHECK: bb15.loopexit2:
; CHECK-NEXT: br label [[BB15]]
; CHECK: bb15:
; CHECK-NEXT: [[TMP16:%.*]] = call i32 (...) @llvm.experimental.deoptimize.i32(i32 17) [ "deopt"() ]
; CHECK-NEXT: ret i32 [[TMP16]]
; CHECK: bb17.loopexit:
; CHECK-NEXT: br label [[BB17:%.*]]
; CHECK: bb17.loopexit3:
; CHECK-NEXT: br label [[BB17]]
; CHECK: bb17:
; CHECK-NEXT: [[TMP18:%.*]] = call i32 (...) @llvm.experimental.deoptimize.i32(i32 6) [ "deopt"() ]
; CHECK-NEXT: ret i32 [[TMP18]]
;
bb:
br label %bb1

bb1: ; preds = %bb13, %bb
%tmp = phi i32 [ -147, %bb ], [ %tmp14, %bb13 ]
br label %bb2

bb2: ; preds = %bb12, %bb1
%tmp3 = phi i32 [ undef, %bb1 ], [ %tmp4, %bb12 ]
%tmp4 = add nsw i32 %tmp3, %tmp
br label %bb5

bb5: ; preds = %bb2
%tmp6 = icmp eq i32 undef, 33
br i1 %tmp6, label %bb7, label %bb15

bb7: ; preds = %bb5
%tmp8 = sub nsw i32 %tmp3, undef
%tmp9 = icmp eq i32 %tmp8, 0
br i1 %tmp9, label %bb10, label %bb10

bb10: ; preds = %bb7, %bb7
%tmp11 = icmp eq i8 undef, 0
br i1 %tmp11, label %bb12, label %bb17

bb12: ; preds = %bb10
br i1 false, label %bb13, label %bb2

bb13: ; preds = %bb12
%tmp14 = add nsw i32 %tmp, -1
br label %bb1

bb15: ; preds = %bb5
%tmp16 = call i32 (...) @llvm.experimental.deoptimize.i32(i32 17) [ "deopt"() ]
ret i32 %tmp16

bb17: ; preds = %bb10
%tmp18 = call i32 (...) @llvm.experimental.deoptimize.i32(i32 6) [ "deopt"() ]
ret i32 %tmp18
}

declare i32 @llvm.experimental.deoptimize.i32(...)

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