[llvm] [X86, SimplifyCFG] Support hoisting load/store with conditional faulting (Part II) (PR #108812)

[Shengchen Kan via llvm-commits]

================
@@ -1771,6 +1782,25 @@ bool SimplifyCFGOpt::hoistCommonCodeFromSuccessors(Instruction *TI,
     if (Succ->hasAddressTaken() || !Succ->getSinglePredecessor())
       return false;
 
+  auto *BI = dyn_cast<BranchInst>(TI);
+  if (BI && HoistLoadsStoresWithCondFaulting &&
+      Options.HoistLoadsStoresWithCondFaulting) {
+    SmallVector<Instruction *, 2> SpeculatedConditionalLoadsStores;
+    for (auto *Succ : successors(BB)) {
+      for (Instruction &I : drop_end(*Succ)) {
+        if (!isSafeCheapLoadStore(&I, TTI) ||
+            SpeculatedConditionalLoadsStores.size() ==
+                HoistLoadsStoresWithCondFaultingThreshold)
+          return false;
+        SpeculatedConditionalLoadsStores.push_back(&I);
+      }
+    }
+
+    if (!SpeculatedConditionalLoadsStores.empty())
----------------
KanRobert wrote:

Considering current implementation separates the common instr hoist from load/store hoist,
probably we should move the code to

```C
  if (BI->getSuccessor(0)->getSinglePredecessor()) {
    if (BI->getSuccessor(1)->getSinglePredecessor()) {
      if (HoistCommon && hoistCommonCodeFromSuccessors(
                             BI->getParent(), !Options.HoistCommonInsts))
        return requestResimplify();

     if  (HoistLoadsStoresWithCondFaulting &&
          Options.HoistLoadsStoresWithCondFaulting && hoistConditionalLoadsStores(...)) 
          return requestResimplify();
```

https://github.com/llvm/llvm-project/pull/108812