[llvm] [UndefOrPoison] [CompileTime] Avoid IDom walk unless required. NFC (PR #90092)

[via llvm-commits]

================
@@ -7283,31 +7283,35 @@ static bool isGuaranteedNotToBeUndefOrPoison(
   // BB1:
   //   CtxI ; V cannot be undef or poison here
   auto *Dominator = DNode->getIDom();
-  while (Dominator) {
-    auto *TI = Dominator->getBlock()->getTerminator();
-
-    Value *Cond = nullptr;
-    if (auto BI = dyn_cast_or_null<BranchInst>(TI)) {
-      if (BI->isConditional())
-        Cond = BI->getCondition();
-    } else if (auto SI = dyn_cast_or_null<SwitchInst>(TI)) {
-      Cond = SI->getCondition();
-    }
+  // This check is purely for compile time reasons: we can skip the IDom walk
+  // if what we are checking for includes undef and the value is not a boolean.
+  if (!includesUndef(Kind) || V->getType()->isIntOrIntVectorTy(1))
+    while (Dominator) {
+      auto *TI = Dominator->getBlock()->getTerminator();
+
+      Value *Cond = nullptr;
+      if (auto BI = dyn_cast_or_null<BranchInst>(TI)) {
+        if (BI->isConditional())
+          Cond = BI->getCondition();
+      } else if (auto SI = dyn_cast_or_null<SwitchInst>(TI)) {
----------------
annamthomas wrote:

err, yes, thanks :) 
Actually, I still this skipping the code entirely (apart from adding the limit to idoms) might be useful for non-integer values (for example: trying to prove noundef for pointer loads across phis, which we do downstream). 
I checked how many lit tests in transform directory can skip this code entirely (added an assert if the Value is non-integer when we reach this IDom walk) : ~100 tests and some of them in LoopVectorizer are pointer Values.  

https://github.com/llvm/llvm-project/pull/90092