[llvm] [SCEVDivision] Prevent propagation of incorrect no-wrap flags (PR #154745)

[Ryotaro Kasuga via llvm-commits]

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@@ -479,14 +479,16 @@ for.cond.cleanup:                                 ; preds = %for.cond.cleanup3,
 ;;    for (int k = 1; k < o; k++)
 ;;      = A[i*m*o + j*o + k]
 ;;     A[i*m*o + j*o + k - 1] =
+;;
+;; FIXME: Currently fails to infer nsw for the SCEV `{0,+,1}<for.body8>`
 define void @t8(i32 %n, i32 %m, i32 %o, ptr nocapture %A) {
 ; CHECK-LABEL: 't8'
 ; CHECK-NEXT:  Src: %0 = load i32, ptr %arrayidx, align 4 --> Dst: %0 = load i32, ptr %arrayidx, align 4
 ; CHECK-NEXT:    da analyze - none!
 ; CHECK-NEXT:  Src: %0 = load i32, ptr %arrayidx, align 4 --> Dst: store i32 %add12, ptr %arrayidx2, align 4
-; CHECK-NEXT:    da analyze - consistent anti [0 0 1]!
+; CHECK-NEXT:    da analyze - anti [* * *|<]!
 ; CHECK-NEXT:  Src: store i32 %add12, ptr %arrayidx2, align 4 --> Dst: store i32 %add12, ptr %arrayidx2, align 4
-; CHECK-NEXT:    da analyze - none!
+; CHECK-NEXT:    da analyze - output [* * *]!
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kasuga-fj wrote:

The essential portion of the IR is as follows:

```llvm
preheader:
  %guard = icmp sgt i32 %o, 0
  br i1 %guard, label %loop, label %exit

loop:
  %i = phi i32 [ 1, %preheader ], [ %inc, %loop ]
  ...
  %inc = add nuw nsw i32 %i, 1
  %exitcond = icmp eq i32 %inc, %o
  br i1 %exitcond, label %exit, label %body

exit:
  ...
```

>From the loop-guard and the induction variable, we know the following:
- `0 <s %o`
- `{1,+,1}<%loop> <s %o`
- `{1,+,1}<%loop>` is nsw and nuw

IIUIC, in principle, we can deduce that `{0,+,1}<%loop>` is also nsw and nuw, but now the inference fails. Are there any good ways to address this case, or do we need to implement a separate inference specifically for it?

https://github.com/llvm/llvm-project/pull/154745