[llvm] [InstCombine] Handle trunc i1 pattern in eq-of-parts fold (PR #112704)

[Yingwei Zheng via llvm-commits]

================
@@ -3538,6 +3546,9 @@ Value *InstCombinerImpl::foldBooleanAndOr(Value *LHS, Value *RHS,
       if (Value *Res = foldLogicOfFCmps(LHSCmp, RHSCmp, IsAnd, IsLogical))
         return Res;
 
+  if (Value *Res = foldEqOfParts(LHS, RHS, IsAnd))
----------------
dtcxzyw wrote:

Regression:
```
define i1 @jv_identical(i64 %0, i64 %2) {
   %.sroa.08.0.extract.trunc = trunc i64 %0 to i8
   %.sroa.311.0.extract.shift = lshr i64 %0, 16
   %.sroa.311.0.extract.trunc = trunc i64 %.sroa.311.0.extract.shift to i16
   %.sroa.0.0.extract.trunc = trunc i64 %2 to i8
   %.sroa.37.0.extract.shift = lshr i64 %2, 16
   %.sroa.37.0.extract.trunc = trunc i64 %.sroa.37.0.extract.shift to i16
   %.not = icmp eq i8 %.sroa.08.0.extract.trunc, %.sroa.0.0.extract.trunc
   %.not2 = icmp eq i16 %.sroa.311.0.extract.trunc, %.sroa.37.0.extract.trunc
   %or.cond = and i1 %.not, %.not2
   %.not3.unshifted = xor i64 %2, %0
   %.not3 = icmp ult i64 %.not3.unshifted, 4294967296
   %or.cond15 = and i1 %.not3, %or.cond
   ret i1 %or.cond15
}
```
Before:
```
define i1 @jv_identical(i64 %0, i64 %1) {
  %.sroa.08.0.extract.trunc = trunc i64 %0 to i8
  %.sroa.311.0.extract.shift = lshr i64 %0, 16
  %.sroa.311.0.extract.trunc = trunc i64 %.sroa.311.0.extract.shift to i16
  %.sroa.0.0.extract.trunc = trunc i64 %1 to i8
  %.sroa.37.0.extract.shift = lshr i64 %1, 16
  %.sroa.37.0.extract.trunc = trunc i64 %.sroa.37.0.extract.shift to i16
  %.not = icmp eq i8 %.sroa.08.0.extract.trunc, %.sroa.0.0.extract.trunc
  %.not2 = icmp eq i16 %.sroa.311.0.extract.trunc, %.sroa.37.0.extract.trunc
  %or.cond = and i1 %.not, %.not2
  %.not3.unshifted = xor i64 %1, %0
  %.not3 = icmp ult i64 %.not3.unshifted, 4294967296
  %or.cond15 = and i1 %.not3, %or.cond
  ret i1 %or.cond15
}
```
After:
```
define i1 @jv_identical(i64 %0, i64 %1) {
  %.sroa.08.0.extract.trunc = trunc i64 %0 to i8
  %.sroa.0.0.extract.trunc = trunc i64 %1 to i8
  %.not = icmp eq i8 %.sroa.08.0.extract.trunc, %.sroa.0.0.extract.trunc
  %.unshifted = xor i64 %1, %0
  %3 = icmp ult i64 %.unshifted, 65536
  %or.cond15 = and i1 %.not, %3
  ret i1 %or.cond15
}
```

I think this fold should be moved before https://github.com/llvm/llvm-project/blob/e9eec14bb3566f6578950797559de98678f16985/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp#L3446-L3448

https://github.com/llvm/llvm-project/pull/112704