GlobalOpt: Drop code for handling pointer bitcasts

[nikic]

Won't this also remove the ability to look through addrspacecasts?

[arsenm]

In D149291#4307575, @nikic wrote:

Won't this also remove the ability to look through addrspacecasts?

Yes, but I'm not entirely sure that's a bad thing. We're certainly missing test coverage for this.

If we have a null pointer in addrspace(0), cast to a non-0 address space pointer and accessed, can we assume it would trap? My interpretation of the LangRef is ptr addrspace(0) null cannot be addrspacecasted to produce a dereferenceable result so this would be OK (so long as it's not a volatile access)

[arsenm]

Should restrict this to just addrspacecast. Plus there's some other bitcast handling code to trim

[aeubanks]

lgtm

[arsenm]

b52db60cbbb2b258acb4aad056aba7ad3ca572fa

[arsenm]

Apparently I got confused and closed the wrong revision, this is really f3059e223dc137ee4111f6e3bb45e7613d6ff7d5

llvm/lib/Transforms/IPO/GlobalOpt.cpp

for (const User *U : V->users()) {
     } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
       if (CI->getCalledOperand() != V) {
         return false;  // Not calling the ptr
       }
     } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
       if (II->getCalledOperand() != V) {
         return false;  // Not calling the ptr
       }
-    } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
-      if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
     } else if (const AddrSpaceCastInst *CI = dyn_cast<AddrSpaceCastInst>(U)) {
       if (!AllUsesOfValueWillTrapIfNull(CI, PHIs))
         return false;
     } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
       if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
     } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
       // If we've already seen this phi node, ignore it, it has already been
       // checked.
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
             CB->setArgOperand(i, NewV);
           }
 
         if (PassedAsArg) {
           // Being passed as an argument also.  Be careful to not invalidate UI!
           UI = V->user_begin();
         }
       }
-    } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
-      Changed |= OptimizeAwayTrappingUsesOfValue(CI,
-                                ConstantExpr::getCast(CI->getOpcode(),
-                                                      NewV, CI->getType()));
+    } else if (AddrSpaceCastInst *CI = dyn_cast<AddrSpaceCastInst>(I)) {
+      Changed |= OptimizeAwayTrappingUsesOfValue(
+          CI, ConstantExpr::getAddrSpaceCast(NewV, CI->getType()));
       if (CI->use_empty()) {
         Changed = true;
         CI->eraseFromParent();
       }
     } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
       // Should handle GEP here.
       SmallVector<Constant*, 8> Idxs;
       Idxs.reserve(GEPI->getNumOperands()-1);