Yingwei Zheng f7ef0721d6 [SCEV] Do not allow refinement in the rewriting of BEValue (#117152) ...

See the following case:
```
; bin/opt -passes="print<scalar-evolution>" test.ll --disable-output
define i32 @widget() {
b:
  br label %b1

b1:                                              ; preds = %b5, %b
  %phi = phi i32 [ 0, %b ], [ %udiv6, %b5 ]
  %phi2 = phi i32 [ 1, %b ], [ %add, %b5 ]
  %icmp = icmp eq i32 %phi, 0
  br i1 %icmp, label %b3, label %b8

b3:                                              ; preds = %b1
  %udiv = udiv i32 10, %phi2
  %urem = urem i32 %udiv, 10
  %icmp4 = icmp eq i32 %urem, 0
  br i1 %icmp4, label %b7, label %b5

b5:                                              ; preds = %b3
  %udiv6 = udiv i32 %phi2, 0
  %add = add i32 %phi2, 1
  br label %b1

b7:                                              ; preds = %b3
  ret i32 5

b8:                                              ; preds = %b1
  ret i32 7
}
```
```
%phi2 = phi i32 [ 1, %b ], [ %add, %b5 ] -->  {1,+,1}<nuw><nsw><%b1>
%udiv6 = udiv i32 %phi2, 0 --> ({1,+,1}<nuw><nsw><%b1> /u 0)
%phi = phi i32 [ 0, %b ], [ %udiv6, %b5 ] --> ({0,+,1}<nuw><nsw><%b1> /u 0)
```
`ScalarEvolution::createAddRecFromPHI` gives a wrong SCEV result for
`%phi`:

d7d6fb1804/llvm/lib/Analysis/ScalarEvolution.cpp (L5926-L5950)
It converts `phi(0, ({1,+,1}<nuw><nsw><%b1> /u 0))` into `phi(0 / 0,
({1,+,1}<nuw><nsw><%b1> /u 0))`. Then it simplifies the expr into
`{0,+,1}<nuw><nsw><%b1> /u 0`.

As we did in
acd700a24b,
this patch disallows udiv simplification if we cannot prove that the
denominator is a well-defined non-zero value.

Fixes https://github.com/llvm/llvm-project/issues/117133.

2024-12-01 20:11:09 +08:00

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