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.
101 lines
4.1 KiB
LLVM
101 lines
4.1 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 -cache-line-size=64 -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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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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@A = common global [100 x [100 x i32]] zeroinitializer
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@B = common global [100 x i32] zeroinitializer
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@C = common global [100 x [100 x i32]] zeroinitializer
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@D = common global [100 x [100 x [100 x i32]]] zeroinitializer
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@T = internal global [100 x double] zeroinitializer, align 4
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@Arr = internal global [1000 x [1000 x i32]] zeroinitializer, align 4
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; Test that a flow dependency in outer loop doesn't prevent interchange in
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; loops i and j.
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;
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; for (int k = 0; k < 100; ++k) {
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; T[k] = fn1();
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; for (int i = 0; i < 1000; ++i)
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; for(int j = 1; j < 1000; ++j)
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; Arr[j][i] = Arr[j][i]+k;
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; fn2(T[k]);
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; }
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;
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; So, loops InnerLoopId = 2 and OuterLoopId = 1 should be interchanged,
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; but not InnerLoopId = 1 and OuterLoopId = 0.
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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: interchange_09
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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: NotTightlyNested
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; CHECK-NEXT: Function: interchange_09
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; CHECK-NEXT: Args:
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; CHECK-NEXT: - String: Cannot interchange loops because they are not tightly nested.
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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: interchange_09
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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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define void @interchange_09(i32 %k) {
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entry:
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br label %for.body
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for.cond.cleanup: ; preds = %for.cond.cleanup4
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ret void
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for.body: ; preds = %for.cond.cleanup4, %entry
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%indvars.iv45 = phi i64 [ 0, %entry ], [ %indvars.iv.next46, %for.cond.cleanup4 ]
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%call = call double @fn1()
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%arrayidx = getelementptr inbounds [100 x double], ptr @T, i64 0, i64 %indvars.iv45
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store double %call, ptr %arrayidx, align 8
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br label %for.cond6.preheader
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for.cond6.preheader: ; preds = %for.cond.cleanup8, %for.body
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%indvars.iv42 = phi i64 [ 0, %for.body ], [ %indvars.iv.next43, %for.cond.cleanup8 ]
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br label %for.body9
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for.cond.cleanup4: ; preds = %for.cond.cleanup8
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%tmp = load double, ptr %arrayidx, align 8
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call void @fn2(double %tmp)
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%indvars.iv.next46 = add nuw nsw i64 %indvars.iv45, 1
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%exitcond47 = icmp ne i64 %indvars.iv.next46, 100
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br i1 %exitcond47, label %for.body, label %for.cond.cleanup
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for.cond.cleanup8: ; preds = %for.body9
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%indvars.iv.next43 = add nuw nsw i64 %indvars.iv42, 1
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%exitcond44 = icmp ne i64 %indvars.iv.next43, 1000
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br i1 %exitcond44, label %for.cond6.preheader, label %for.cond.cleanup4
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for.body9: ; preds = %for.body9, %for.cond6.preheader
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%indvars.iv = phi i64 [ 1, %for.cond6.preheader ], [ %indvars.iv.next, %for.body9 ]
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%arrayidx13 = getelementptr inbounds [1000 x [1000 x i32]], ptr @Arr, i64 0, i64 %indvars.iv, i64 %indvars.iv42
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%t1 = load i32, ptr %arrayidx13, align 4
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%t2 = trunc i64 %indvars.iv45 to i32
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%add = add nsw i32 %t1, %t2
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store i32 %add, ptr %arrayidx13, align 4
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%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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%exitcond = icmp ne i64 %indvars.iv.next, 1000
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br i1 %exitcond, label %for.body9, label %for.cond.cleanup8
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}
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declare double @fn1() readnone
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declare void @fn2(double) readnone
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