[DSE] Use helper for unwind check (NFCI)

This should be no functional change, as the cases supported by the
helper and the cases supported by DSE are currently the same, the
code structure is just slightly different.

Author: nikic

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

@@ -756,9 +756,8 @@ struct DSEState {
   SmallVector<MemoryDef *, 64> MemDefs;
   // Any that should be skipped as they are already deleted
   SmallPtrSet<MemoryAccess *, 4> SkipStores;
-  // Keep track of all of the objects that are invisible to the caller before
-  // the function returns.
-  DenseMap<const Value *, bool> InvisibleToCallerBeforeRet;
+  // Keep track whether a given object is captured before return or not.
+  DenseMap<const Value *, bool> CapturedBeforeReturn;
   // Keep track of all of the objects that are invisible to the caller after
   // the function returns.
   DenseMap<const Value *, bool> InvisibleToCallerAfterRet;
@@ -801,12 +800,8 @@ struct DSEState {
     // Treat byval or inalloca arguments the same as Allocas, stores to them are
     // dead at the end of the function.
     for (Argument &AI : F.args())
-      if (AI.hasPassPointeeByValueCopyAttr()) {
-        // For byval, the caller doesn't know the address of the allocation.
-        if (AI.hasByValAttr())
-          InvisibleToCallerBeforeRet.insert({&AI, true});
+      if (AI.hasPassPointeeByValueCopyAttr())
         InvisibleToCallerAfterRet.insert({&AI, true});
-      }
 
     // Collect whether there is any irreducible control flow in the function.
     ContainsIrreducibleLoops = mayContainIrreducibleControl(F, &LI);
@@ -953,7 +948,7 @@ struct DSEState {
       return true;
     auto I = InvisibleToCallerAfterRet.insert({V, false});
     if (I.second) {
-      if (!isInvisibleToCallerBeforeRet(V)) {
+      if (!isInvisibleToCallerOnUnwind(V)) {
         I.first->second = false;
       } else if (isNoAliasCall(V)) {
         I.first->second = !PointerMayBeCaptured(V, true, false);
@@ -962,17 +957,21 @@ struct DSEState {
     return I.first->second;
   }
 
-  bool isInvisibleToCallerBeforeRet(const Value *V) {
-    if (isa<AllocaInst>(V))
+  bool isInvisibleToCallerOnUnwind(const Value *V) {
+    bool RequiresNoCaptureBeforeUnwind;
+    if (!isNotVisibleOnUnwind(V, RequiresNoCaptureBeforeUnwind))
+      return false;
+    if (!RequiresNoCaptureBeforeUnwind)
       return true;
-    auto I = InvisibleToCallerBeforeRet.insert({V, false});
-    if (I.second && isNoAliasCall(V))
+
+    auto I = CapturedBeforeReturn.insert({V, true});
+    if (I.second)
       // NOTE: This could be made more precise by PointerMayBeCapturedBefore
       // with the killing MemoryDef. But we refrain from doing so for now to
       // limit compile-time and this does not cause any changes to the number
       // of stores removed on a large test set in practice.
-      I.first->second = !PointerMayBeCaptured(V, false, true);
-    return I.first->second;
+      I.first->second = PointerMayBeCaptured(V, false, true);
+    return !I.first->second;
   }
 
   Optional<MemoryLocation> getLocForWrite(Instruction *I) const {
@@ -1260,8 +1259,7 @@ struct DSEState {
       MemoryDef *CurrentDef = cast<MemoryDef>(Current);
       Instruction *CurrentI = CurrentDef->getMemoryInst();
 
-      if (canSkipDef(CurrentDef,
-                     !isInvisibleToCallerBeforeRet(KillingUndObj))) {
+      if (canSkipDef(CurrentDef, !isInvisibleToCallerOnUnwind(KillingUndObj))) {
         CanOptimize = false;
         continue;
       }
@@ -1433,7 +1431,7 @@ struct DSEState {
         continue;
       }
 
-      if (UseInst->mayThrow() && !isInvisibleToCallerBeforeRet(KillingUndObj)) {
+      if (UseInst->mayThrow() && !isInvisibleToCallerOnUnwind(KillingUndObj)) {
         LLVM_DEBUG(dbgs() << "  ... found throwing instruction\n");
         return None;
       }
@@ -1614,7 +1612,7 @@ struct DSEState {
     // First see if we can ignore it by using the fact that KillingI is an
     // alloca/alloca like object that is not visible to the caller during
     // execution of the function.
-    if (KillingUndObj && isInvisibleToCallerBeforeRet(KillingUndObj))
+    if (KillingUndObj && isInvisibleToCallerOnUnwind(KillingUndObj))
       return false;
 
     if (KillingI->getParent() == DeadI->getParent())
@@ -1630,7 +1628,7 @@ struct DSEState {
   bool isDSEBarrier(const Value *KillingUndObj, Instruction *DeadI) {
     // If DeadI may throw it acts as a barrier, unless we are to an
     // alloca/alloca like object that does not escape.
-    if (DeadI->mayThrow() && !isInvisibleToCallerBeforeRet(KillingUndObj))
+    if (DeadI->mayThrow() && !isInvisibleToCallerOnUnwind(KillingUndObj))
       return true;
 
     // If DeadI is an atomic load/store stronger than monotonic, do not try to