GVN-hoist: avoid calling MemoryLocation::get() on a call (PR30499)

[sebpop]

Summary

For some reason in the cleanup or in the change I did to use the MemorySSA.cpp interface, I introduced more calls to MemoryLocation::get() without checking whether the instruction was a call.
I will apply this patch on top of yesterday's fix (that got reverted.)
This should fix the ICE in Chromium builds.

lib/Transforms/Utils/MemorySSA.cpp

static bool instructionClobbersQuery(MemoryDef *MD,
   }
 
   return AA.getModRefInfo(DefInst, UseLoc) & MRI_Mod;
 }
 
 // Return true when MD may alias MU, return false otherwise.
 bool defClobbersUseOrDef(MemoryDef *MD, const MemoryUseOrDef *MU,
                          AliasAnalysis &AA) {
-  Instruction *Insn = MU->getMemoryInst();
-  return instructionClobbersQuery(MD, MemoryLocation::get(Insn), Insn, AA);
+  Instruction *UseInst = MU->getMemoryInst();
+  MemoryLocation UseLoc;
+  if (ImmutableCallSite(UseInst))
+    UseLoc = MemoryLocation();
+  else
+    UseLoc = MemoryLocation::get(UseInst);
+  return instructionClobbersQuery(MD, UseLoc, UseInst, AA);
 }
 }
 
 namespace {
 struct UpwardsMemoryQuery {
   // True if our original query started off as a call
   bool IsCall;
   // The pointer location we started the query with. This will be empty if