[llvm] [SCEV] Do not allow refinement in the rewriting of BEValue (PR #117152)

[Yingwei Zheng via llvm-commits]

================
@@ -0,0 +1,97 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -disable-output "-passes=print<scalar-evolution>" < %s 2>&1 | FileCheck %s
+
+define i32 @widget() {
+; CHECK-LABEL: 'widget'
+; CHECK-NEXT:  Classifying expressions for: @widget
+; CHECK-NEXT:    %phi = phi i32 [ 0, %b ], [ %udiv6, %b5 ]
+; CHECK-NEXT:    --> %phi U: [0,1) S: [0,1) Exits: <<Unknown>> LoopDispositions: { %b1: Variant }
+; CHECK-NEXT:    %phi2 = phi i32 [ 1, %b ], [ %add, %b5 ]
+; CHECK-NEXT:    --> {1,+,1}<nuw><nsw><%b1> U: [1,2) S: [1,2) Exits: <<Unknown>> LoopDispositions: { %b1: Computable }
+; CHECK-NEXT:    %udiv = udiv i32 10, %phi2
+; CHECK-NEXT:    --> (10 /u {1,+,1}<nuw><nsw><%b1>) U: [10,11) S: [10,11) Exits: <<Unknown>> LoopDispositions: { %b1: Computable }
+; CHECK-NEXT:    %urem = urem i32 %udiv, 10
+; CHECK-NEXT:    --> ((-10 * ((10 /u {1,+,1}<nuw><nsw><%b1>) /u 10))<nuw><nsw> + (10 /u {1,+,1}<nuw><nsw><%b1>)) U: [0,1) S: [0,1) Exits: <<Unknown>> LoopDispositions: { %b1: Computable }
+; CHECK-NEXT:    %udiv6 = udiv i32 %phi2, 0
+; CHECK-NEXT:    --> ({1,+,1}<nuw><nsw><%b1> /u 0) U: empty-set S: empty-set Exits: <<Unknown>> LoopDispositions: { %b1: Computable }
+; CHECK-NEXT:    %add = add i32 %phi2, 1
+; CHECK-NEXT:    --> {2,+,1}<nuw><nsw><%b1> U: [2,3) S: [2,3) Exits: <<Unknown>> LoopDispositions: { %b1: Computable }
+; CHECK-NEXT:  Determining loop execution counts for: @widget
+; CHECK-NEXT:  Loop %b1: <multiple exits> Unpredictable backedge-taken count.
+; CHECK-NEXT:    exit count for b1: ***COULDNOTCOMPUTE***
+; CHECK-NEXT:    exit count for b3: i32 0
+; CHECK-NEXT:  Loop %b1: constant max backedge-taken count is i32 0
+; CHECK-NEXT:  Loop %b1: symbolic max backedge-taken count is i32 0
+; CHECK-NEXT:    symbolic max exit count for b1: ***COULDNOTCOMPUTE***
+; CHECK-NEXT:    symbolic max exit count for b3: i32 0
+;
+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
+}
+
+; Don't fold %indvar2 into (zext {0,+,1}) * %a
+define i64 @test_poisonous(i64 %a, i32 %n) {
----------------
dtcxzyw wrote:

Before:
```
Printing analysis 'Scalar Evolution Analysis' for function 'test':
Classifying expressions for: @test
  %indvar1 = phi i32 [ 0, %entry ], [ %indvar1.next, %loop.body ]
  -->  {0,+,1}<%loop.body> U: full-set S: full-set              Exits: <<Unknown>>              LoopDispositions: { %loop.body: Computable }
  %indvar2 = phi i64 [ 0, %entry ], [ %mul, %loop.body ]
  -->  ((zext i32 {0,+,1}<%loop.body> to i64) * %a) U: full-set S: full-set             Exits: <<Unknown>>              LoopDispositions: { %loop.body: Computable }
  %indvar1.next = add i32 %indvar1, 1
  -->  {1,+,1}<%loop.body> U: full-set S: full-set              Exits: <<Unknown>>              LoopDispositions: { %loop.body: Computable }
  %ext = zext i32 %indvar1.next to i64
  -->  (zext i32 {1,+,1}<%loop.body> to i64) U: [0,4294967296) S: [0,4294967296)                Exits: <<Unknown>>              LoopDispositions: { %loop.body: Computable }
  %mul = mul i64 %ext, %a
  -->  ((zext i32 {1,+,1}<%loop.body> to i64) * %a) U: full-set S: full-set             Exits: <<Unknown>>              LoopDispositions: { %loop.body: Computable }
```

https://github.com/llvm/llvm-project/pull/117152