[llvm] [InstCombine] Fold (X == 0 ? Y : 0) | X to X == 0 ? Y : X (PR #138373)

[via llvm-commits]

================
@@ -3658,6 +3658,15 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
       return R;
   }
 
+  // (X == 0 ? Y : 0) | X -> X == 0 ? Y : X
+  // X | (X == 0 ? Y : 0) -> X == 0 ? Y : X
+  for (Value *Op : {Op0, Op1}) {
+    if (auto *SI = dyn_cast<SelectInst>(Op)) {
+      if (auto *R = FoldOpIntoSelect(I, SI, /* FoldWithMultiUse */ false))
+        return R;
+    }
+  }
----------------
YLChenZ wrote:

If we ignore the sext/zext case and lift constant restriction, then do the test I get the following result:
```
llvm test
********************
Timed Out Tests (6):
  LLVM :: Transforms/InstCombine/conditional-variable-length-signext-after-high-bit-extract.ll
  LLVM :: Transforms/InstCombine/icmp-and-lowbit-mask.ll
  LLVM :: Transforms/InstCombine/logical-select-inseltpoison.ll
  LLVM :: Transforms/InstCombine/logical-select.ll
  LLVM :: Transforms/InstCombine/vec_sext.ll
  LLVM :: Transforms/PhaseOrdering/vector-select.ll

********************
Failed Tests (16):
  LLVM :: Transforms/InstCombine/binop-phi-operands.ll
  LLVM :: Transforms/InstCombine/binop-select.ll
  LLVM :: Transforms/InstCombine/dont-distribute-phi.ll
  LLVM :: Transforms/InstCombine/fmul.ll
  LLVM :: Transforms/InstCombine/free-inversion.ll
  LLVM :: Transforms/InstCombine/icmp-or-of-select-with-zero.ll
  LLVM :: Transforms/InstCombine/mul-inseltpoison.ll
  LLVM :: Transforms/InstCombine/or-select-zero-icmp.ll
  LLVM :: Transforms/InstCombine/pr82877.ll
  LLVM :: Transforms/InstCombine/recurrence.ll
  LLVM :: Transforms/InstCombine/select-cmp-cttz-ctlz.ll
  LLVM :: Transforms/InstCombine/select.ll
  LLVM :: Transforms/InstCombine/simplify-demanded-fpclass.ll
  LLVM :: Transforms/InstCombine/sub-gep.ll
  LLVM :: Transforms/InstCombine/xor.ll
  LLVM :: Transforms/PhaseOrdering/AArch64/predicated-reduction.ll
  
clang test
********************
Timed Out Tests (1):
  Clang :: CodeGen/SystemZ/builtins-systemz-zvector5.c
  
--timeout=100

```
I think the failed may be well handled , but the timed out is tricky, and there should seem to be infinite loops when folding.  I don't know if I'm right about this.

https://github.com/llvm/llvm-project/pull/138373