[llvm] [LAA] Always use DepCands when grouping runtime checks. (PR #91196)

[Igor Kirillov via llvm-commits]

================
@@ -1303,17 +1303,38 @@ bool AccessAnalysis::createCheckForAccess(
 }
 
 bool AccessAnalysis::canCheckPtrAtRT(
-    RuntimePointerChecking &RtCheck, Loop *TheLoop,
+    RuntimePointerChecking &RtCheck, ScalarEvolution *SE, Loop *TheLoop,
     const DenseMap<Value *, const SCEV *> &StridesMap, Value *&UncomputablePtr,
-    bool AllowPartial) {
+    bool AllowPartial, const MemoryDepChecker &DepChecker) {
   // Find pointers with computable bounds. We are going to use this information
   // to place a runtime bound check.
   bool CanDoRT = true;
 
   bool MayNeedRTCheck = false;
   if (!IsRTCheckAnalysisNeeded) return true;
 
-  bool IsDepCheckNeeded = isDependencyCheckNeeded();
+  if (auto *Deps = DepChecker.getDependences()) {
+    // If there are unknown dependences, this means runtime checks are needed to
+    // ensure there's no overlap between accesses to the same underlying object.
+    // Remove the equivalence classes containing both source and destination
+    // accesses from DepCands. This ensures runtime checks will be generated
+    // between those accesses and prevents them from being grouped together.
+    for (const auto &Dep : *Deps) {
+      if (Dep.Type != MemoryDepChecker::Dependence::Unknown) {
+        assert(MemoryDepChecker::Dependence::isSafeForVectorization(Dep.Type) ==
+                   MemoryDepChecker::VectorizationSafetyStatus::Safe &&
+               "Should only skip safe dependences");
+        continue;
+      }
+      Instruction *Src = Dep.getSource(DepChecker);
+      Instruction *Dst = Dep.getDestination(DepChecker);
+      DepCands.eraseClass({getPointerOperand(Src), Src->mayWriteToMemory()});
+      DepCands.eraseClass({getPointerOperand(Dst), Dst->mayWriteToMemory()});
----------------
igogo-x86 wrote:

Adding a comment here - or removing this line and adding a comment instead - would be helpful for future readers

https://github.com/llvm/llvm-project/pull/91196