281028e37c
LoopInterchange uses the bubble-sort fashion algorithm to sort the loops in a loop nest. For two loops `A` and `B`, it calls `isProfitable(A, B)` to determine whether these loops should be exchanged. The result of `isProfitable(A, B)` should be conservative, that is, it should return true only when we are sure exchanging `A` and `B` will improve performance. If it's not conservative enough, it's possible that a subsequent `isProfitable(B, A)` will also return true, in which case LoopInterchange will undo its previous transformation. To avoid such cases, `isProfitable(B, A)` must not return true if `isProfitable(A, B)` returned true in the past. However, the current implementation can be in such a situation. This patch resolves it by correcting the handling of two loops that have the same cache cost. This resolve the problem mentioned in https://github.com/llvm/llvm-project/pull/118267#issuecomment-2510759354.
82 lines
3.0 KiB
LLVM
82 lines
3.0 KiB
LLVM
; RUN: opt < %s -passes=loop-interchange -cache-line-size=1 -pass-remarks-output=%t -disable-output \
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; RUN: -verify-dom-info -verify-loop-info
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; RUN: FileCheck -input-file %t %s
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; Test that loop-interchange doesn't undo its own transoformation. This is
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; the case when the cost computed by CacheCost is the same for the loop of `j`
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; and `k`.
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;
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; #define N 4
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; int a[N*N][N*N][N*N];
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; void f() {
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; for (int i = 0; i < N; i++)
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; for (int j = 1; j < 2*N; j++)
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; for (int k = 1; k < 2*N; k++)
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; a[i][k+1][j-1] -= a[i+N-1][k][j];
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; }
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; CHECK: --- !Passed
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; CHECK-NEXT: Pass: loop-interchange
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; CHECK-NEXT: Name: Interchanged
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; CHECK-NEXT: Function: f
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; CHECK-NEXT: Args:
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; CHECK-NEXT: - String: Loop interchanged with enclosing loop.
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; CHECK-NEXT: ...
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; CHECK-NEXT: --- !Missed
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; CHECK-NEXT: Pass: loop-interchange
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; CHECK-NEXT: Name: Dependence
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; CHECK-NEXT: Function: f
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; CHECK-NEXT: Args:
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; CHECK-NEXT: - String: Cannot interchange loops due to dependences.
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; CHECK-NEXT: ...
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; CHECK-NEXT: --- !Missed
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; CHECK-NEXT: Pass: loop-interchange
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; CHECK-NEXT: Name: InterchangeNotProfitable
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; CHECK-NEXT: Function: f
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; CHECK-NEXT: Args:
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; CHECK-NEXT: - String: Interchanging loops is not considered to improve cache locality nor vectorization.
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; CHECK-NEXT: ...
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@a = dso_local local_unnamed_addr global [16 x [16 x [16 x i32]]] zeroinitializer, align 4
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define dso_local void @f() {
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entry:
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br label %for.cond1.preheader
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for.cond1.preheader:
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%indvars.iv46 = phi i64 [ 0, %entry ], [ %indvars.iv.next47, %for.cond.cleanup3 ]
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%0 = add nuw nsw i64 %indvars.iv46, 3
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br label %for.cond5.preheader
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for.cond5.preheader:
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%indvars.iv41 = phi i64 [ 1, %for.cond1.preheader ], [ %indvars.iv.next42, %for.cond.cleanup7 ]
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%1 = add nsw i64 %indvars.iv41, -1
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br label %for.body8
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for.cond.cleanup3:
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%indvars.iv.next47 = add nuw nsw i64 %indvars.iv46, 1
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%exitcond50 = icmp ne i64 %indvars.iv.next47, 4
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br i1 %exitcond50, label %for.cond1.preheader, label %for.cond.cleanup
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for.cond.cleanup7:
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%indvars.iv.next42 = add nuw nsw i64 %indvars.iv41, 1
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%exitcond45 = icmp ne i64 %indvars.iv.next42, 8
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br i1 %exitcond45, label %for.cond5.preheader, label %for.cond.cleanup3
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for.body8:
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%indvars.iv = phi i64 [ 1, %for.cond5.preheader ], [ %indvars.iv.next, %for.body8 ]
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%arrayidx12 = getelementptr inbounds nuw [16 x [16 x [16 x i32]]], ptr @a, i64 0, i64 %0, i64 %indvars.iv, i64 %indvars.iv41
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%2 = load i32, ptr %arrayidx12, align 4
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%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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%arrayidx20 = getelementptr inbounds [16 x [16 x [16 x i32]]], ptr @a, i64 0, i64 %indvars.iv46, i64 %indvars.iv.next, i64 %1
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%3 = load i32, ptr %arrayidx20, align 4
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%sub21 = sub nsw i32 %3, %2
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store i32 %sub21, ptr %arrayidx20, align 4
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%exitcond = icmp ne i64 %indvars.iv.next, 8
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br i1 %exitcond, label %for.body8, label %for.cond.cleanup7
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for.cond.cleanup:
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ret void
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}
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