[IR][OpaquePointers] Properly print cmpxchg with pointer operands.

[dantrushin]

Summary

With opaque pointers address of pointer variable and its value have
same type (ptr). As a result, cmpxchg is printed without values
types in LLVM assembly and cannot be read back. Add AtomicCmpXchg
to the list of instructions which always have operand types printed.

[nikic]

LG

llvm/lib/IR/AsmWriter.cpp

if (isa<BranchInst>(I) && cast<BranchInst>(I).isConditional()) {
     }
 
     // PrintAllTypes - Instructions who have operands of all the same type
     // omit the type from all but the first operand.  If the instruction has
     // different type operands (for example br), then they are all printed.
     bool PrintAllTypes = false;
     Type *TheType = Operand->getType();
 
-    // Select, Store and ShuffleVector always print all types.
-    if (isa<SelectInst>(I) || isa<StoreInst>(I) || isa<ShuffleVectorInst>(I)
-        || isa<ReturnInst>(I)) {
+    // Select, Store, ShuffleVector and CmpXchg always print all types.
+    if (isa<SelectInst>(I) || isa<StoreInst>(I) || isa<ShuffleVectorInst>(I) ||
+        isa<ReturnInst>(I) || isa<AtomicCmpXchgInst>(I)) {
       PrintAllTypes = true;
     } else {
       for (unsigned i = 1, E = I.getNumOperands(); i != E; ++i) {
         Operand = I.getOperand(i);
         // note that Operand shouldn't be null, but the test helps make dump()
         // more tolerant of malformed IR
         if (Operand && Operand->getType() != TheType) {
           PrintAllTypes = true;    // We have differing types!  Print them all!

llvm/test/Assembler/opaque-ptr.ll

 ; CHECK: define void @cmpxchg(ptr %p, i32 %a, i32 %b)
 ; CHECK:     %val_success = cmpxchg ptr %p, i32 %a, i32 %b acq_rel monotonic
 ; CHECK:     ret void
 define void @cmpxchg(ptr %p, i32 %a, i32 %b) {
     %val_success = cmpxchg ptr %p, i32 %a, i32 %b acq_rel monotonic
     ret void
 }
 
+; CHECK: define void @cmpxchg_ptr(ptr %p, ptr %a, ptr %b)
+; CHECK:     %val_success = cmpxchg ptr %p, ptr %a, ptr %b acq_rel monotonic
+; CHECK:     ret void
+define void @cmpxchg_ptr(ptr %p, ptr %a, ptr %b) {
+    %val_success = cmpxchg ptr %p, ptr %a, ptr %b acq_rel monotonic
+    ret void
+}
+
 ; CHECK: define void @atomicrmw(ptr %a, i32 %i)
 ; CHECK:     %b = atomicrmw add ptr %a, i32 %i acquire
 ; CHECK:     ret void
 define void @atomicrmw(ptr %a, i32 %i) {
     %b = atomicrmw add ptr %a, i32 %i acquire
     ret void
 }