[LV] Use more accurate getSCEV/MemChecks in GeneratedRTCheck::hasChecks.

Update hasChecks to use getSCEV/MemRuntimeChecks(), which automatically
handles checking for known-false checks.

This improves a few cases where we previously did not add metadata to
disable runtime unrolling, due to runtime checks, even though no runtime
checks are needed.

Author: fhahn

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -2001,7 +2001,7 @@ class GeneratedRTChecks {
 
   /// Retrieves the SCEVCheckCond and SCEVCheckBlock that were generated as IR
   /// outside VPlan.
-  std::pair<Value *, BasicBlock *> getSCEVChecks() {
+  std::pair<Value *, BasicBlock *> getSCEVChecks() const {
     using namespace llvm::PatternMatch;
     if (!SCEVCheckCond || match(SCEVCheckCond, m_ZeroInt()))
       return {nullptr, nullptr};
@@ -2011,7 +2011,7 @@ class GeneratedRTChecks {
 
   /// Retrieves the MemCheckCond and MemCheckBlock that were generated as IR
   /// outside VPlan.
-  std::pair<Value *, BasicBlock *> getMemRuntimeChecks() {
+  std::pair<Value *, BasicBlock *> getMemRuntimeChecks() const {
     using namespace llvm::PatternMatch;
     if (MemRuntimeCheckCond && match(MemRuntimeCheckCond, m_ZeroInt()))
       return {nullptr, nullptr};
@@ -2020,9 +2020,7 @@ class GeneratedRTChecks {
 
   /// Return true if any runtime checks have been added
   bool hasChecks() const {
-    using namespace llvm::PatternMatch;
-    return (SCEVCheckCond && !match(SCEVCheckCond, m_ZeroInt())) ||
-           MemRuntimeCheckCond;
+    return getSCEVChecks().first || getMemRuntimeChecks().first;
   }
 };
 } // namespace

llvm/test/Transforms/LoopVectorize/runtime-check-needed-but-empty.ll

@@ -71,7 +71,7 @@ exit:
   ret void
 }
 
-; FIXME: !llvm.loop.unroll.runtime.disable metadata should be added to the
+; !llvm.loop.unroll.runtime.disable metadata should be added to the
 ; scalar loop, as there are no runtime checks needed (or they can be proven
 ; false).
 define void @diff_memcheck_known_false_for_vf_4(ptr %B, ptr %A, ptr %end) {
@@ -151,5 +151,5 @@ exit:
 ; CHECK: [[META2]] = !{!"llvm.loop.unroll.runtime.disable"}
 ; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META1]]}
 ; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META1]], [[META2]]}
-; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META1]]}
+; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META2]], [[META1]]}
 ;.