[llvm] [LV] Add initial legality checks for early exit loops with side effects (PR #145663)

[Florian Hahn via llvm-commits]

================
@@ -1813,6 +1840,113 @@ bool LoopVectorizationLegality::isVectorizableEarlyExitLoop() {
                        "backedge taken count: "
                     << *SymbolicMaxBTC << '\n');
   UncountableExitingBB = SingleUncountableExitingBlock;
+  UncountableExitWithSideEffects = HasSideEffects;
+  return true;
+}
+
+bool LoopVectorizationLegality::canUncountableExitConditionLoadBeMoved(
+    BasicBlock *ExitingBlock) {
+  LoadInst *CriticalUncountableExitConditionLoad = nullptr;
+
+  // Try to find a load in the critical path for the uncountable exit condition.
+  // This is currently matching about the simplest form we can, expecting
+  // only one in-loop load, the result of which is directly compared against
+  // a loop-invariant value.
+  // FIXME: We're insisting on a single use for now, because otherwise we will
+  // need to make PHI nodes for other users. That can be done once the initial
+  // transform code lands.
+  auto *Br = cast<BranchInst>(ExitingBlock->getTerminator());
+
+  using namespace llvm::PatternMatch;
+  Value *L = nullptr;
+  Value *R = nullptr;
+  if (!match(Br->getCondition(),
+             m_OneUse(m_ICmp(m_OneUse(m_Value(L)), (m_Value(R)))))) {
----------------
fhahn wrote:

I think you should able to match the load directly here using something like below

```suggestion
             m_OneUse(m_ICmp(m_Instruction(L, m_OneUse(m_Load(L))), (m_Value(R)))))) {
```


https://github.com/llvm/llvm-project/pull/145663