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[LAA] Add a test case to show incorrect dependency classification (NFC). #70473

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Oct 31, 2023
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[LAA] Add a test case to show incorrect dependency classification (NFC). #70473

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40 changes: 40 additions & 0 deletions llvm/test/Analysis/LoopAccessAnalysis/forward-negative-step.ll
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; RUN: opt -passes='print<access-info>' -disable-output < %s 2>&1 | FileCheck %s

target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"

; FIXME: This should be vectorizable

; void vectorizable_Read_Write(int *A) {
; for (unsigned i = 1022; i >= 0; i--)
; A[i+1] = A[i] + 1;
; }

; CHECK: function 'vectorizable_Read_Write':
; CHECK-NEXT: for.body:
; CHECK-NEXT: Report: unsafe dependent memory operations in loop
; CHECK-NEXT: Forward loop carried data dependence that prevents store-to-load forwarding.
; CHECK-NEXT: Dependences:
; CHECK-NEXT: ForwardButPreventsForwarding:
; CHECK-NEXT: %0 = load i32, ptr %arrayidx, align 4 ->
; CHECK-NEXT: store i32 %add, ptr %gep, align 4

define void @vectorizable_Read_Write(ptr nocapture %A) {
entry:
%invariant.gep = getelementptr i32, ptr %A, i64 1
br label %for.body

for.cond.cleanup:
ret void

for.body:
%indvars.iv = phi i64 [ 1022, %entry ], [ %indvars.iv.next, %for.body ]
%arrayidx = getelementptr inbounds i32, ptr %A, i64 %indvars.iv
%0 = load i32, ptr %arrayidx, align 4
%add = add nsw i32 %0, 1
%gep = getelementptr i32, ptr %invariant.gep, i64 %indvars.iv
store i32 %add, ptr %gep, align 4
%indvars.iv.next = add nsw i64 %indvars.iv, -1
%cmp.not = icmp eq i64 %indvars.iv, 0
br i1 %cmp.not, label %for.cond.cleanup, label %for.body
}