[PATCH] D106099: [DependenceAnalysis] Guard analysis using getPointerBase()

[Artem Radzikhovskyy via Phabricator via llvm-commits]

artemrad added inline comments.


================
Comment at: llvm/lib/Analysis/DependenceAnalysis.cpp:3556
   LLVM_DEBUG(dbgs() << "    DstSCEV = " << *DstSCEV << "\n");
+  if (SE->getPointerBase(SrcSCEV) != SE->getPointerBase(DstSCEV)) {
+    // If two pointers have different bases, trying to analyze indexes won't
----------------
This seems like a subset of cases we should be filtering out. Please also add checks for the access width being unaligned with the store/load size. In this case the base pointers are different but the accesses can still overlap. This case will not be caught by DependenceAnalysis. 


```
define void @z0(i32* %A, i64 %n) nounwind uwtable ssp {
entry:
  %arrayidx = getelementptr inbounds i32, i32* %A, i64 %n
  %arrayidx_cast = bitcast i32* %arrayidx to i64*
  store i64 0, i64* %arrayidx_cast, align 4

; CHECK: da analyze - confused!
; CHECK: da analyze - confused!
; CHECK: da analyze - confused!
; CHECK: da analyze - none
; CHECK: da analyze - confused!
; CHECK: da analyze - confused!

  %add1 = add i64 %n, 1
  %arrayidx2 = getelementptr inbounds i32, i32* %A, i64 %add1
  %0 = load i32, i32* %arrayidx2, align 4
 
  ; Even if the load and store types are the same, if their
  ; alignments are smaller than the store size and they are
  ; accesses through something other than a straightforward
  ; gep, they can still overlap, as this access shows
  %arrayidx2_cast = bitcast i32* %arrayidx2 to i64*
  %1 = load i64, i64* %arrayidx2_cast, align 4
  ret void
}
```






Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D106099/new/

https://reviews.llvm.org/D106099