[llvm] [ValueTracking] Refactor `isKnownNonEqualFromContext` (PR #127388)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

Case 2 (improvement):
```
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define void @_ZN3net17HpackHuffmanTable17BuildDecodeTablesERKSt6vectorINS_18HpackHuffmanSymbolESaIS2_EE(ptr %0) {
entry:
  %1 = load i8, ptr %0, align 1
  br label %while.cond

while.cond:                                       ; preds = %for.body125, %while.cond, %entry
  %2 = load i8, ptr %0, align 1
  %cmp97.not = icmp eq i8 %2, 0
  %cmp101 = icmp uge i8 %2, %1
  %or.cond.not1 = select i1 %cmp97.not, i1 true, i1 %cmp101
  br i1 %or.cond.not1, label %while.cond, label %for.body125

for.body125:                                      ; preds = %for.body125, %while.cond
  %cmp124.not.old = icmp eq i8 %1, %2
  call void @use(i1 %cmp124.not.old)
  br i1 %cmp124.not.old, label %while.cond, label %for.body125
}

declare void @use(i1)
```
With this patch, we iterate over related dominating conditions of `%2` (`%or.cond.not1`) and fold `%cmp124.not.old` into false.


https://github.com/llvm/llvm-project/pull/127388