48d7cc6ae2
SCEV makes a logical mistake when handling EitherMayExit in case when both conditions must be met to exit the loop. The mistake looks like follows: "if condition `A` fails within at most `X` first iterations, and `B` fails within at most `Y` first iterations, then `A & B` fails at most within `min (X, Y)` first iterations". This is wrong, because both of them must fail at the same time. Simple example illustrating this is following: we have an IV with step 1, condition `A` = "IV is even", condition `B` = "IV is odd". Both `A` and `B` will fail within first two iterations. But it doesn't mean that both of them will fail within first two first iterations at the same time, which would mean that IV is neither even nor odd at the same time within first 2 iterations. We can only do so for known exact BE counts, but not for max. Differential Revision: https://reviews.llvm.org/D91942 Reviewed By: nikic
100 lines
4.3 KiB
LLVM
100 lines
4.3 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
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; RUN: opt < %s -analyze -enable-new-pm=0 -scalar-evolution | FileCheck %s
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; RUN: opt < %s -disable-output "-passes=print<scalar-evolution>" 2>&1 | FileCheck %s
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; Tests demonstrate the bug reported as PR48225 by Congzhe Cao.
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; When %boolcond = false and %cond = 0:
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; - %cond.false.on.first.iter is false on 1st iteration;
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; - %cond.false.on.second.iter is false on 2nd iteration;
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; - Therefore, their AND is false on first two iterations, and the backedge is taken twice.
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; 'max backedge-taken count is 1' is a bug caused by wrong treatment of AND
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; condition in the computation logic. It should be 2.
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define void @test_and(i1 %boolcond) {
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; CHECK-LABEL: 'test_and'
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; CHECK-NEXT: Classifying expressions for: @test_and
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; CHECK-NEXT: %conv = zext i1 %boolcond to i32
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; CHECK-NEXT: --> (zext i1 %boolcond to i32) U: [0,2) S: [0,2)
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; CHECK-NEXT: %iv = phi i32 [ 0, %entry ], [ %inc, %backedge ]
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; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%loop> U: [0,3) S: [0,3) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
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; CHECK-NEXT: %or.cond = and i1 %cond.false.on.first.iter, %cond.false.on.second.iter
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; CHECK-NEXT: --> %or.cond U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
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; CHECK-NEXT: %inc = add nuw nsw i32 %iv, 1
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; CHECK-NEXT: --> {1,+,1}<nuw><nsw><%loop> U: [1,4) S: [1,4) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
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; CHECK-NEXT: Determining loop execution counts for: @test_and
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; CHECK-NEXT: Loop %loop: <multiple exits> Unpredictable backedge-taken count.
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; CHECK-NEXT: exit count for loop: 2
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; CHECK-NEXT: exit count for backedge: ***COULDNOTCOMPUTE***
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; CHECK-NEXT: Loop %loop: max backedge-taken count is 2
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; CHECK-NEXT: Loop %loop: Unpredictable predicated backedge-taken count.
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;
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entry:
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%conv = zext i1 %boolcond to i32
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br label %loop
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loop:
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%iv = phi i32 [ 0, %entry ], [ %inc, %backedge ]
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%cmp = icmp ult i32 %iv, 2
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br i1 %cmp, label %backedge, label %for.end
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backedge:
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%cond.false.on.first.iter = icmp ne i32 %iv, 0
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%cond.false.on.second.iter = icmp eq i32 %iv, %conv
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%or.cond = and i1 %cond.false.on.first.iter, %cond.false.on.second.iter
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%inc = add nuw nsw i32 %iv, 1
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br i1 %or.cond, label %exit, label %loop
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exit:
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unreachable
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for.end:
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ret void
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}
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; When %boolcond = false and %cond = 0:
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; - %cond.true.on.first.iter is true on 1st iteration;
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; - %cond.true.on.second.iter is true on 2nd iteration;
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; - Therefore, their OR is true on first two iterations, and the backedge is taken twice.
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; 'max backedge-taken count is 1' is a bug caused by wrong treatment of OR
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; condition in the computation logic. It should be 2.
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define void @test_or(i1 %boolcond) {
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; CHECK-LABEL: 'test_or'
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; CHECK-NEXT: Classifying expressions for: @test_or
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; CHECK-NEXT: %conv = zext i1 %boolcond to i32
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; CHECK-NEXT: --> (zext i1 %boolcond to i32) U: [0,2) S: [0,2)
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; CHECK-NEXT: %iv = phi i32 [ 0, %entry ], [ %inc, %backedge ]
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; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%loop> U: [0,3) S: [0,3) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
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; CHECK-NEXT: %or.cond = or i1 %cond.true.on.first.iter, %cond.true.on.second.iter
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; CHECK-NEXT: --> %or.cond U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
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; CHECK-NEXT: %inc = add nuw nsw i32 %iv, 1
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; CHECK-NEXT: --> {1,+,1}<nuw><nsw><%loop> U: [1,4) S: [1,4) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
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; CHECK-NEXT: Determining loop execution counts for: @test_or
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; CHECK-NEXT: Loop %loop: <multiple exits> Unpredictable backedge-taken count.
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; CHECK-NEXT: exit count for loop: 2
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; CHECK-NEXT: exit count for backedge: ***COULDNOTCOMPUTE***
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; CHECK-NEXT: Loop %loop: max backedge-taken count is 2
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; CHECK-NEXT: Loop %loop: Unpredictable predicated backedge-taken count.
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;
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entry:
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%conv = zext i1 %boolcond to i32
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br label %loop
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loop:
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%iv = phi i32 [ 0, %entry ], [ %inc, %backedge ]
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%cmp = icmp ult i32 %iv, 2
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br i1 %cmp, label %backedge, label %for.end
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backedge:
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%cond.true.on.first.iter = icmp eq i32 %iv, 0
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%cond.true.on.second.iter = icmp ne i32 %iv, %conv
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%or.cond = or i1 %cond.true.on.first.iter, %cond.true.on.second.iter
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%inc = add nuw nsw i32 %iv, 1
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br i1 %or.cond, label %loop, label %exit
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exit:
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unreachable
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for.end:
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ret void
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}
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