Initialize IsFast* values

[bcain]

Summary

We must initialize these values in case some targets do not assign to them in allowsMemoryAccess().

[RKSimon]

LGTM

[bcain]

This change seemed inocent enough. Were the false values here the right defaults?

Could this regression really be due to this change?

http://lab.llvm.org:8011/builders/openmp-gcc-x86_64-linux-debian/builds/5090/steps/test-openmp/logs/FAIL%3A%20libomp%3A%3Abug_nested_proxy_task.c

[RKSimon]

In D76156#1922562, @bcain wrote:

This change seemed inocent enough. Were the false values here the right defaults?

Yes, we tend to check for IsFast=true after most successful allowsMemoryAccess calls so false is the better default. But really if a target allowsMemoryAccess implementation is going to return true it should always explicitly set the IsFast value as well.

Could this regression really be due to this change?

http://lab.llvm.org:8011/builders/openmp-gcc-x86_64-linux-debian/builds/5090/steps/test-openmp/logs/FAIL%3A%20libomp%3A%3Abug_nested_proxy_task.c

The openmp buildbots are notoriously unreliable - my recommendation for those bots is always to wait for another build to see if the red just goes away.....

[RKSimon]

This landed at rGad7b930bd18a

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

if (IsExtractVecSrc) {
         unsigned FirstStoreAS = FirstInChain->getAddressSpace();
         unsigned FirstStoreAlign = FirstInChain->getAlignment();
         unsigned NumStoresToMerge = 1;
         for (unsigned i = 0; i < NumConsecutiveStores; ++i) {
           // Find a legal type for the vector store.
           unsigned Elts = (i + 1) * NumMemElts;
           EVT Ty =
               EVT::getVectorVT(*DAG.getContext(), MemVT.getScalarType(), Elts);
-          bool IsFast;
+          bool IsFast = false;
 
           // Break early when size is too large to be legal.
           if (Ty.getSizeInBits() > MaximumLegalStoreInBits)
             break;
 
           if (TLI.isTypeLegal(Ty) &&
               TLI.canMergeStoresTo(FirstStoreAS, Ty, DAG) &&
               TLI.allowsMemoryAccess(Context, DL, Ty,
while (NumConsecutiveStores >= 2 && LoadNodes.size() >= 2) {
         // Find a legal type for the vector store.
         unsigned Elts = (i + 1) * NumMemElts;
         EVT StoreTy = EVT::getVectorVT(Context, MemVT.getScalarType(), Elts);
 
         // Break early when size is too large to be legal.
         if (StoreTy.getSizeInBits() > MaximumLegalStoreInBits)
           break;
 
-        bool IsFastSt, IsFastLd;
+        bool IsFastSt = false;
+        bool IsFastLd = false;
         if (TLI.isTypeLegal(StoreTy) &&
             TLI.canMergeStoresTo(FirstStoreAS, StoreTy, DAG) &&
             TLI.allowsMemoryAccess(Context, DL, StoreTy,
                                    *FirstInChain->getMemOperand(), &IsFastSt) &&
             IsFastSt &&
             TLI.allowsMemoryAccess(Context, DL, StoreTy,
                                    *FirstLoad->getMemOperand(), &IsFastLd) &&
             IsFastLd) {