[llvm] [SCEV] Check whether the start is non-zero in `ScalarEvolution::howFarToZero` (PR #131522)

[Yingwei Zheng via llvm-commits]

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@@ -329,10 +329,9 @@ define void @ne_nsw_nonneg_step(ptr nocapture %A, i32 %n, i32 %s) mustprogress {
 ;
 ; CHECK-LABEL: 'ne_nsw_nonneg_step'
 ; CHECK-NEXT:  Determining loop execution counts for: @ne_nsw_nonneg_step
-; CHECK-NEXT:  Loop %for.body: backedge-taken count is (((-1 * %s) + %n) /u %s)
-; CHECK-NEXT:  Loop %for.body: constant max backedge-taken count is i32 -1
-; CHECK-NEXT:  Loop %for.body: symbolic max backedge-taken count is (((-1 * %s) + %n) /u %s)
-; CHECK-NEXT:  Loop %for.body: Trip multiple is 1
+; CHECK-NEXT:  Loop %for.body: Unpredictable backedge-taken count.
+; CHECK-NEXT:  Loop %for.body: Unpredictable constant max backedge-taken count.
+; CHECK-NEXT:  Loop %for.body: Unpredictable symbolic max backedge-taken count.
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dtcxzyw wrote:

Oh, sorry, the start value is `(zext i1 %tobool2.not to i32)`.


https://github.com/llvm/llvm-project/pull/131522