[Scalar] Avoid repeated hash lookups (NFC) (#132330)

Author: kazutakahirata

llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp

@@ -1182,11 +1182,12 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &Cache,
       for (unsigned i = 0; i < NumPHIValues; i++) {
         Value *InVal = PN->getIncomingValue(i);
         BasicBlock *InBB = PN->getIncomingBlock(i);
-        if (!BlockToValue.count(InBB))
-          BlockToValue[InBB] = getBaseForInput(InVal, InBB->getTerminator());
+        auto [It, Inserted] = BlockToValue.try_emplace(InBB);
+        if (Inserted)
+          It->second = getBaseForInput(InVal, InBB->getTerminator());
         else {
 #ifndef NDEBUG
-          Value *OldBase = BlockToValue[InBB];
+          Value *OldBase = It->second;
           Value *Base = getBaseForInput(InVal, nullptr);
 
           // We can't use `stripPointerCasts` instead of this function because
@@ -1206,7 +1207,7 @@ static Value *findBasePointer(Value *I, DefiningValueMapTy &Cache,
                  "findBaseOrBDV should be pure!");
 #endif
         }
-        Value *Base = BlockToValue[InBB];
+        Value *Base = It->second;
         BasePHI->setIncomingValue(i, Base);
       }
     } else if (SelectInst *BaseSI =
@@ -1545,9 +1546,10 @@ static void CreateGCRelocates(ArrayRef<Value *> LiveVariables,
     Value *LiveIdx = Builder.getInt32(i);
 
     Type *Ty = LiveVariables[i]->getType();
-    if (!TypeToDeclMap.count(Ty))
-      TypeToDeclMap[Ty] = getGCRelocateDecl(Ty);
-    Function *GCRelocateDecl = TypeToDeclMap[Ty];
+    auto [It, Inserted] = TypeToDeclMap.try_emplace(Ty);
+    if (Inserted)
+      It->second = getGCRelocateDecl(Ty);
+    Function *GCRelocateDecl = It->second;
 
     // only specify a debug name if we can give a useful one
     CallInst *Reloc = Builder.CreateCall(
@@ -2378,9 +2380,9 @@ findRematerializationCandidates(PointerToBaseTy PointerToBase,
 
     // Handle the scenario where the RootOfChain is not equal to the
     // Base Value, but they are essentially the same phi values.
-    if (RootOfChain != PointerToBase[Derived]) {
+    if (Value *BaseVal = PointerToBase[Derived]; RootOfChain != BaseVal) {
       PHINode *OrigRootPhi = dyn_cast<PHINode>(RootOfChain);
-      PHINode *AlternateRootPhi = dyn_cast<PHINode>(PointerToBase[Derived]);
+      PHINode *AlternateRootPhi = dyn_cast<PHINode>(BaseVal);
       if (!OrigRootPhi || !AlternateRootPhi)
         continue;
       // PHI nodes that have the same incoming values, and belonging to the same