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clang-p2996/llvm/test/Analysis/ScalarEvolution/incorrect-exit-count.ll
Philip Reames f39978b84f [SCEV] Correctly propagate nowrap flags across scopes when folding invariant add through addrec 
This fixes a violation of the wrap flag rules introduced in c4048d8f. This is an alternate fix to D106852.

The basic problem being fixed is that we infer a set of flags which is valid at some inner scope S1 (usually by correctly propagating them from IR), and then (incorrectly) extend them to a SCEV in scope S2 where S1 != S2. This is not in general safe per the wrap flags semantics recently defined.

In this patch, I include a simple inference step to handle the case where we can prove that S2 is the preheader of the loop S1, and that entry into S2 implies execution of S1. See the code for a more detailed explanation.

One worry I have with this patch is that I might be over-fitting what shows up in tests - and thus hiding negative impact we'd see in the real world. My best defense is that the rule used here very closely follows the one used to propagate the flags from IR to the inner add to start with, and thus if one is reasonable, so probably is the other. Curious what others think about that piece.

The test diffs are roughly as expected. Mostly analysis only, with two transform changes. Oddly, the result looks better in the loop-idiom test, and I don't understand the PPC output enough to have tell. Nothing terrible looking though. (For context, without the scope inference peephole, the test delta includes a couple of vectorization tests. Again, not super concerning, but slightly more so.)

Differential Revision: https://reviews.llvm.org/D109845
2021-10-03 15:19:33 -07:00

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; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
; RUN: opt -passes='print<scalar-evolution>' < %s -disable-output 2>&1 | FileCheck %s
@b = dso_local global i32 5, align 4
@__const.f.g = private unnamed_addr constant [1 x [4 x i16]] [[4 x i16] [i16 1, i16 0, i16 0, i16 0]], align 2
@a = common dso_local global i32 0, align 4
@c = common dso_local global i32 0, align 4
@d = common dso_local global i32 0, align 4
@e = common dso_local global i32 0, align 4
; When inner.loop is taken as an exiting block of outer.loop, we cannot use the
; addrec of %storemerge1921.3, which is {3, +, -1}<inner.loop>, to calculate the
; exit count because it doesn't belong to outer.loop.
define dso_local i32 @f() {
; CHECK-LABEL: 'f'
; CHECK-NEXT: Classifying expressions for: @f
; CHECK-NEXT: %storemerge23 = phi i32 [ 3, %entry ], [ %dec16, %for.inc13.3 ]
; CHECK-NEXT: --> {3,+,-1}<nsw><%outer.loop> U: [1,4) S: [1,4) Exits: <<Unknown>> LoopDispositions: { %outer.loop: Computable, %for.cond6: Invariant, %inner.loop: Invariant }
; CHECK-NEXT: %storemerge1921 = phi i32 [ 3, %outer.loop ], [ %dec, %for.end ]
; CHECK-NEXT: --> {3,+,-1}<nuw><nsw><%for.cond6> U: [3,4) S: [3,4) Exits: <<Unknown>> LoopDispositions: { %for.cond6: Computable, %outer.loop: Variant }
; CHECK-NEXT: %idxprom20 = zext i32 %storemerge1921 to i64
; CHECK-NEXT: --> {3,+,4294967295}<nuw><nsw><%for.cond6> U: [3,4) S: [3,4) Exits: <<Unknown>> LoopDispositions: { %for.cond6: Computable, %outer.loop: Variant }
; CHECK-NEXT: %arrayidx7 = getelementptr inbounds [1 x [4 x i16]], [1 x [4 x i16]]* @__const.f.g, i64 0, i64 0, i64 %idxprom20
; CHECK-NEXT: --> {(6 + @__const.f.g),+,8589934590}<nuw><%for.cond6> U: [0,-1) S: [-9223372036854775808,9223372036854775807) Exits: <<Unknown>> LoopDispositions: { %for.cond6: Computable, %outer.loop: Variant }
; CHECK-NEXT: %i = load i16, i16* %arrayidx7, align 2
; CHECK-NEXT: --> %i U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %for.cond6: Variant, %outer.loop: Variant }
; CHECK-NEXT: %storemerge1822.lcssa.ph = phi i32 [ 0, %for.cond6 ]
; CHECK-NEXT: --> 0 U: [0,1) S: [0,1)
; CHECK-NEXT: %storemerge1822.lcssa.ph32 = phi i32 [ 3, %inner.loop ]
; CHECK-NEXT: --> 3 U: [3,4) S: [3,4)
; CHECK-NEXT: %storemerge1822.lcssa = phi i32 [ %storemerge1822.lcssa.ph, %if.end.loopexit ], [ %storemerge1822.lcssa.ph32, %if.end.loopexit31 ]
; CHECK-NEXT: --> %storemerge1822.lcssa U: [0,4) S: [0,4)
; CHECK-NEXT: %i1 = load i32, i32* @e, align 4
; CHECK-NEXT: --> %i1 U: full-set S: full-set
; CHECK-NEXT: %i2 = load volatile i32, i32* @b, align 4
; CHECK-NEXT: --> %i2 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %for.cond6: Variant, %outer.loop: Variant }
; CHECK-NEXT: %dec = add nsw i32 %storemerge1921, -1
; CHECK-NEXT: --> {2,+,-1}<nsw><%for.cond6> U: [2,3) S: [2,3) Exits: <<Unknown>> LoopDispositions: { %for.cond6: Computable, %outer.loop: Variant }
; CHECK-NEXT: %inc.lcssa.lcssa = phi i32 [ 4, %for.inc13.3 ]
; CHECK-NEXT: --> 4 U: [4,5) S: [4,5)
; CHECK-NEXT: %retval.0 = phi i32 [ %i1, %if.end ], [ 0, %cleanup.loopexit ]
; CHECK-NEXT: --> %retval.0 U: full-set S: full-set
; CHECK-NEXT: %storemerge1921.3 = phi i32 [ 3, %for.end ], [ %dec.3, %for.end.3 ]
; CHECK-NEXT: --> {3,+,-1}<nuw><nsw><%inner.loop> U: [3,4) S: [3,4) Exits: <<Unknown>> LoopDispositions: { %inner.loop: Computable, %outer.loop: Variant }
; CHECK-NEXT: %idxprom20.3 = zext i32 %storemerge1921.3 to i64
; CHECK-NEXT: --> {3,+,4294967295}<nuw><nsw><%inner.loop> U: [3,4) S: [3,4) Exits: <<Unknown>> LoopDispositions: { %inner.loop: Computable, %outer.loop: Variant }
; CHECK-NEXT: %arrayidx7.3 = getelementptr inbounds [1 x [4 x i16]], [1 x [4 x i16]]* @__const.f.g, i64 0, i64 0, i64 %idxprom20.3
; CHECK-NEXT: --> {(6 + @__const.f.g),+,8589934590}<nuw><%inner.loop> U: [0,-1) S: [-9223372036854775808,9223372036854775807) Exits: <<Unknown>> LoopDispositions: { %inner.loop: Computable, %outer.loop: Variant }
; CHECK-NEXT: %i7 = load i16, i16* %arrayidx7.3, align 2
; CHECK-NEXT: --> %i7 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %inner.loop: Variant, %outer.loop: Variant }
; CHECK-NEXT: %i8 = load volatile i32, i32* @b, align 4
; CHECK-NEXT: --> %i8 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %inner.loop: Variant, %outer.loop: Variant }
; CHECK-NEXT: %dec.3 = add nsw i32 %storemerge1921.3, -1
; CHECK-NEXT: --> {2,+,-1}<nsw><%inner.loop> U: [2,3) S: [2,3) Exits: <<Unknown>> LoopDispositions: { %inner.loop: Computable, %outer.loop: Variant }
; CHECK-NEXT: %storemerge1921.lcssa25.3 = phi i32 [ %storemerge1921.3, %for.end.3 ]
; CHECK-NEXT: --> %storemerge1921.lcssa25.3 U: [3,4) S: [3,4) Exits: <<Unknown>> LoopDispositions: { %outer.loop: Variant, %for.cond6: Invariant, %inner.loop: Invariant }
; CHECK-NEXT: %dec16 = add nsw i32 %storemerge23, -1
; CHECK-NEXT: --> {2,+,-1}<nsw><%outer.loop> U: [0,3) S: [0,3) Exits: <<Unknown>> LoopDispositions: { %outer.loop: Computable, %for.cond6: Invariant, %inner.loop: Invariant }
; CHECK-NEXT: Determining loop execution counts for: @f
; CHECK-NEXT: Loop %for.cond6: <multiple exits> Unpredictable backedge-taken count.
; CHECK-NEXT: exit count for for.cond6: 0
; CHECK-NEXT: exit count for for.end: ***COULDNOTCOMPUTE***
; CHECK-NEXT: Loop %for.cond6: max backedge-taken count is 0
; CHECK-NEXT: Loop %for.cond6: Unpredictable predicated backedge-taken count.
; CHECK-NEXT: Loop %inner.loop: <multiple exits> Unpredictable backedge-taken count.
; CHECK-NEXT: exit count for inner.loop: 0
; CHECK-NEXT: exit count for for.end.3: ***COULDNOTCOMPUTE***
; CHECK-NEXT: Loop %inner.loop: max backedge-taken count is 0
; CHECK-NEXT: Loop %inner.loop: Unpredictable predicated backedge-taken count.
; CHECK-NEXT: Loop %outer.loop: <multiple exits> Unpredictable backedge-taken count.
; CHECK-NEXT: exit count for for.cond6: ***COULDNOTCOMPUTE***
; CHECK-NEXT: exit count for inner.loop: ***COULDNOTCOMPUTE***
; CHECK-NEXT: exit count for for.inc13.3: 2
; CHECK-NEXT: Loop %outer.loop: max backedge-taken count is 2
; CHECK-NEXT: Loop %outer.loop: Unpredictable predicated backedge-taken count.
;
entry:
store i32 3, i32* @a, align 4
br label %outer.loop
outer.loop: ; preds = %for.inc13.3, %entry
%storemerge23 = phi i32 [ 3, %entry ], [ %dec16, %for.inc13.3 ]
br label %for.cond6
for.cond6: ; preds = %for.end, %outer.loop
%storemerge1921 = phi i32 [ 3, %outer.loop ], [ %dec, %for.end ]
%idxprom20 = zext i32 %storemerge1921 to i64
%arrayidx7 = getelementptr inbounds [1 x [4 x i16]], [1 x [4 x i16]]* @__const.f.g, i64 0, i64 0, i64 %idxprom20
%i = load i16, i16* %arrayidx7, align 2
%tobool8 = icmp eq i16 %i, 0
br i1 %tobool8, label %if.end.loopexit, label %for.end
if.end.loopexit: ; preds = %for.cond6
%storemerge1822.lcssa.ph = phi i32 [ 0, %for.cond6 ]
br label %if.end
if.end.loopexit31: ; preds = %inner.loop
%storemerge1822.lcssa.ph32 = phi i32 [ 3, %inner.loop ]
br label %if.end
if.end: ; preds = %if.end.loopexit31, %if.end.loopexit
%storemerge1822.lcssa = phi i32 [ %storemerge1822.lcssa.ph, %if.end.loopexit ], [ %storemerge1822.lcssa.ph32, %if.end.loopexit31 ]
store i32 %storemerge1822.lcssa, i32* @c, align 4
store i32 2, i32* @d, align 4
%i1 = load i32, i32* @e, align 4
br label %cleanup
for.end: ; preds = %for.cond6
%i2 = load volatile i32, i32* @b, align 4
%tobool9 = icmp eq i32 %i2, 0
%dec = add nsw i32 %storemerge1921, -1
br i1 %tobool9, label %for.cond6, label %inner.loop
cleanup.loopexit: ; preds = %for.inc13.3
%inc.lcssa.lcssa = phi i32 [ 4, %for.inc13.3 ]
store i32 %inc.lcssa.lcssa, i32* @c, align 4
br label %cleanup
cleanup: ; preds = %cleanup.loopexit, %if.end
%retval.0 = phi i32 [ %i1, %if.end ], [ 0, %cleanup.loopexit ]
ret i32 %retval.0
inner.loop: ; preds = %for.end.3, %for.end
%storemerge1921.3 = phi i32 [ 3, %for.end ], [ %dec.3, %for.end.3 ]
%idxprom20.3 = zext i32 %storemerge1921.3 to i64
%arrayidx7.3 = getelementptr inbounds [1 x [4 x i16]], [1 x [4 x i16]]* @__const.f.g, i64 0, i64 0, i64 %idxprom20.3
%i7 = load i16, i16* %arrayidx7.3, align 2
%tobool8.3 = icmp eq i16 %i7, 0
br i1 %tobool8.3, label %if.end.loopexit31, label %for.end.3
for.end.3: ; preds = %inner.loop
%i8 = load volatile i32, i32* @b, align 4
%tobool9.3 = icmp eq i32 %i8, 0
%dec.3 = add nsw i32 %storemerge1921.3, -1
br i1 %tobool9.3, label %inner.loop, label %for.inc13.3
for.inc13.3: ; preds = %for.end.3
%storemerge1921.lcssa25.3 = phi i32 [ %storemerge1921.3, %for.end.3 ]
store i32 %storemerge1921.lcssa25.3, i32* @d, align 4
%dec16 = add nsw i32 %storemerge23, -1
store i32 %dec16, i32* @a, align 4
%tobool = icmp eq i32 %dec16, 0
br i1 %tobool, label %cleanup.loopexit, label %outer.loop
}
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