3ad6d1cbe5
As shown in #70473, the following loop was not considered safe to vectorize. When determining the memory access dependencies in a loop which has negative iteration step, we invert the source and sink of the dependence. Perhaps we should just invert the operands to getMinusSCEV(). This way the dependency is not regarded to be true, since the users of the `IsWrite` variables, which correspond to each of the memory accesses, rely on program order and therefore should not be swapped. void vectorizable_Read_Write(int *A) { for (unsigned i = 1022; i >= 0; i--) A[i+1] = A[i] + 1; }
66 lines
2.1 KiB
LLVM
66 lines
2.1 KiB
LLVM
; REQUIRES: asserts
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; RUN: opt -passes='print<access-info>' -debug-only=loop-accesses -disable-output < %s 2>&1 | FileCheck %s
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; void negative_step(int *A) {
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; for (int i = 1022; i >= 0; i--)
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; A[i+1] = A[i] + 1;
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; }
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; CHECK: LAA: Found a loop in negative_step: loop
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; CHECK: LAA: Checking memory dependencies
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; CHECK-NEXT: LAA: Src Scev: {(4092 + %A),+,-4}<nw><%loop>Sink Scev: {(4088 + %A)<nuw>,+,-4}<nw><%loop>(Induction step: -1)
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; CHECK-NEXT: LAA: Distance for store i32 %add, ptr %gep.A.plus.1, align 4 to %l = load i32, ptr %gep.A, align 4: -4
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; CHECK-NEXT: LAA: Dependence is negative
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define void @negative_step(ptr nocapture %A) {
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entry:
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%A.plus.1 = getelementptr i32, ptr %A, i64 1
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br label %loop
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loop:
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%iv = phi i64 [ 1022, %entry ], [ %iv.next, %loop ]
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%gep.A = getelementptr inbounds i32, ptr %A, i64 %iv
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%l = load i32, ptr %gep.A, align 4
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%add = add nsw i32 %l, 1
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%gep.A.plus.1 = getelementptr i32, ptr %A.plus.1, i64 %iv
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store i32 %add, ptr %gep.A.plus.1, align 4
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%iv.next = add nsw i64 %iv, -1
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%cmp.not = icmp eq i64 %iv, 0
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br i1 %cmp.not, label %exit, label %loop
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exit:
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ret void
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}
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; void positive_step(int *A) {
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; for (int i = 1; i < 1024; i++)
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; A[i-1] = A[i] + 1;
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; }
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; CHECK: LAA: Found a loop in positive_step: loop
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; CHECK: LAA: Checking memory dependencies
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; CHECK-NEXT: LAA: Src Scev: {(4 + %A)<nuw>,+,4}<nuw><%loop>Sink Scev: {%A,+,4}<nw><%loop>(Induction step: 1)
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; CHECK-NEXT: LAA: Distance for %l = load i32, ptr %gep.A, align 4 to store i32 %add, ptr %gep.A.minus.1, align 4: -4
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; CHECK-NEXT: LAA: Dependence is negative
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define void @positive_step(ptr nocapture %A) {
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entry:
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%A.minus.1 = getelementptr i32, ptr %A, i64 -1
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br label %loop
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loop:
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%iv = phi i64 [ 1, %entry ], [ %iv.next, %loop ]
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%gep.A = getelementptr inbounds i32, ptr %A, i64 %iv
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%l = load i32, ptr %gep.A, align 4
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%add = add nsw i32 %l, 1
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%gep.A.minus.1 = getelementptr i32, ptr %A.minus.1, i64 %iv
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store i32 %add, ptr %gep.A.minus.1, align 4
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%iv.next = add nsw i64 %iv, 1
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%cmp.not = icmp eq i64 %iv, 1024
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br i1 %cmp.not, label %exit, label %loop
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exit:
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ret void
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}
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