456ec1c2f4
We are not handling 'S' scalar dependencies correctly and have at least the following miscompiles related to that: [LoopInterchange] incorrect handling of scalar dependencies and dependence vectors starting with ">" #54176 [LoopInterchange] Interchange breaks program correctness #46867 [LoopInterchange] Loops should not interchanged due to dependencies #47259 [LoopInterchange] Loops should not interchanged due to control flow #47401 This patch does no longer insert the "S" dependency/direction into the dependency matrix, so a dependency is never "S". We seem to have forgotten what the exact meaning is of this dependency type, and don't see why it should be treated differently. We prefer correctness over incorrect and more aggressive results. I.e., this prevents the miscompiles at the expense of handling less cases, i.e. making interchange more pessimistic. However, some of the cases that are now rejected for dependence analysis reasons, were rejected before too but for other reasons (e.g. profitability). So at least for the llvm regression tests, the number of regression are very reasonable. This should be a stopgap. We would like to get interchange enabled by default and thus prefer correctness over unsafe transforms, and later see if we can get solve the regressions.
85 lines
3.8 KiB
LLVM
85 lines
3.8 KiB
LLVM
; Remove 'S' Scalar Dependencies #119345
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; Scalar dependencies are not handled correctly, so they were removed to avoid
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; miscompiles. The loop nest in this test case used to be interchanged, but it's
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; no longer triggering. XFAIL'ing this test to indicate that this test should
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; interchanged if scalar deps are handled correctly.
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;
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; XFAIL: *
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; RUN: opt < %s -passes=loop-interchange -verify-dom-info -verify-loop-info -pass-remarks-output=%t -disable-output
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; RUN: FileCheck -input-file %t %s
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@a = common global i32 0, align 4
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@d = common dso_local local_unnamed_addr global [1 x [6 x i32]] zeroinitializer, align 4
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; After interchanging the innermost and the middle loop, we should not continue
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; doing interchange for the (new) middle loop and the outermost loop, because of
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; values defined in the new innermost loop not available in the exiting block of
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; the entire loop nest.
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;
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; CHECK: --- !Passed
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; CHECK: Pass: loop-interchange
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; CHECK: Name: Interchanged
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; CHECK: Function: innermost_latch_uses_values_in_middle_header
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; CHECK: Args:
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; CHECK: - String: Loop interchanged with enclosing loop.
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; CHECK: ...
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; CHECK: --- !Missed
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; CHECK: Pass: loop-interchange
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; CHECK: Name: UnsupportedInnerLatchPHI
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; CHECK: Function: innermost_latch_uses_values_in_middle_header
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; CHECK: Args:
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; CHECK: - String: Cannot interchange loops because unsupported PHI nodes found in inner loop latch.
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; CHECK: ...
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; CHECK: --- !Missed
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; CHECK: Pass: loop-interchange
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; CHECK: Name: UnsupportedExitPHI
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; CHECK: Function: innermost_latch_uses_values_in_middle_header
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; CHECK: Args:
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; CHECK: - String: Found unsupported PHI node in loop exit.
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; CHECK: ...
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;
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define void @innermost_latch_uses_values_in_middle_header() {
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entry:
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%0 = load i32, ptr @a, align 4
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%b = add i32 80, 1
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br label %outermost.header
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outermost.header: ; preds = %outermost.latch, %entry
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%indvar.outermost = phi i32 [ 10, %entry ], [ %indvar.outermost.next, %outermost.latch ]
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%tobool71.i = icmp eq i32 %0, 0
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br i1 %tobool71.i, label %middle.header, label %outermost.latch
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middle.header: ; preds = %middle.latch, %outermost.header
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%indvar.middle = phi i64 [ 4, %outermost.header ], [ %indvar.middle.next, %middle.latch ]
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%indvar.middle.wide = zext i32 %b to i64 ; a def in the middle header
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br label %innermost.header
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innermost.header: ; preds = %middle.header, %innermost.latch
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%indvar.innermost = phi i64 [ %indvar.innermost.next, %innermost.latch ], [ 4, %middle.header ]
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br label %innermost.body
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innermost.body: ; preds = %innermost.header
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%arrayidx9.i = getelementptr inbounds [1 x [6 x i32]], ptr @d, i64 0, i64 %indvar.innermost, i64 %indvar.middle
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store i32 0, ptr %arrayidx9.i, align 4
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br label %innermost.latch
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innermost.latch: ; preds = %innermost.body
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%indvar.innermost.next = add nsw i64 %indvar.innermost, 1
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%tobool5.i = icmp eq i64 %indvar.innermost.next, %indvar.middle.wide ; corresponding use in the innermost latch
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br i1 %tobool5.i, label %middle.latch, label %innermost.header
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middle.latch: ; preds = %innermost.latch
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%indvar.middle.next = add nsw i64 %indvar.middle, -1
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%tobool2.i = icmp eq i64 %indvar.middle.next, 0
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br i1 %tobool2.i, label %outermost.latch, label %middle.header
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outermost.latch: ; preds = %middle.latch, %outermost.header
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%indvar.outermost.next = add nsw i32 %indvar.outermost, -5
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%tobool.i = icmp eq i32 %indvar.outermost.next, 0
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br i1 %tobool.i, label %outermost.exit, label %outermost.header
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outermost.exit: ; preds = %outermost.latch
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ret void
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}
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