7d21d7395c
Currently the loop access analysis classifies this loop as unsafe to
vectorize because the memory dependencies are
'ForwardButPreventsForwarding'. However, the access pattern is
'write-after-read' with no subsequent read accessing the written memory
locations. I can't see how store-to-load forwarding is applicable here.
void vectorizable_Read_Write(int *A) {
for (unsigned i = 1022; i >= 0; i--)
A[i+1] = A[i] + 1;
}
41 lines
1.3 KiB
LLVM
41 lines
1.3 KiB
LLVM
; RUN: opt -passes='print<access-info>' -disable-output < %s 2>&1 | FileCheck %s
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target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
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; FIXME: This should be vectorizable
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; void vectorizable_Read_Write(int *A) {
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; for (unsigned i = 1022; i >= 0; i--)
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; A[i+1] = A[i] + 1;
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; }
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; CHECK: function 'vectorizable_Read_Write':
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; CHECK-NEXT: for.body:
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; CHECK-NEXT: Report: unsafe dependent memory operations in loop
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; CHECK-NEXT: Forward loop carried data dependence that prevents store-to-load forwarding.
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; CHECK-NEXT: Dependences:
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; CHECK-NEXT: ForwardButPreventsForwarding:
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; CHECK-NEXT: %0 = load i32, ptr %arrayidx, align 4 ->
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; CHECK-NEXT: store i32 %add, ptr %gep, align 4
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define void @vectorizable_Read_Write(ptr nocapture %A) {
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entry:
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%invariant.gep = getelementptr i32, ptr %A, i64 1
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br label %for.body
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for.cond.cleanup:
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ret void
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for.body:
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%indvars.iv = phi i64 [ 1022, %entry ], [ %indvars.iv.next, %for.body ]
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%arrayidx = getelementptr inbounds i32, ptr %A, i64 %indvars.iv
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%0 = load i32, ptr %arrayidx, align 4
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%add = add nsw i32 %0, 1
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%gep = getelementptr i32, ptr %invariant.gep, i64 %indvars.iv
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store i32 %add, ptr %gep, align 4
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%indvars.iv.next = add nsw i64 %indvars.iv, -1
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%cmp.not = icmp eq i64 %indvars.iv, 0
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br i1 %cmp.not, label %for.cond.cleanup, label %for.body
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}
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