[Verifier] add test case for callbr

[nickdesaulniers]

Summary

Check the list of indirect targets; if there's an indirect target
that's not also listed in the operand list, we have a problem.

I'm seeing something funny going on in a particular transform. This
added check is helping me pinpoint it in opt.

[efriedma]

Is this documented in LangRef somewhere? I'm not seeing anything that indicates the blockaddress has to be an operand of the callbr, and I'm not sure why it would be necessary.

[nickdesaulniers]

Good point; while I think this kind of invariant exists from asm goto C code that gets generated, I don't think LLVM IR in general requires such an invariant. This was mostly used to help me debug https://reviews.llvm.org/D64101.

llvm/lib/IR/Verifier.cpp

void Verifier::visitCallBrInst(CallBrInst &CBI) {
   for (unsigned i = 0, e = CBI.getNumOperands(); i != e; ++i) {
     Assert(i >= CBI.getNumArgOperands() || !isa<BasicBlock>(CBI.getOperand(i)),
            "Using an unescaped label as a callbr argument!", &CBI);
     if (isa<BasicBlock>(CBI.getOperand(i)))
       for (unsigned j = i + 1; j != e; ++j)
         Assert(CBI.getOperand(i) != CBI.getOperand(j),
                "Duplicate callbr destination!", &CBI);
   }
+  for (auto *BB : CBI.getIndirectDests()) {
+    BlockAddress *BA = BlockAddress::get(BB);
+    bool Found = false;
+    for (unsigned i = 0, e = CBI.getNumOperands(); i != e; ++i)
+      if (CBI.getOperand(i) == BA) {
+        Found = true;
+        break;
+      }
+    Assert(Found, "Did not find indirect destination in callbr operand list",
+           &CBI);
+  }
 
   visitTerminator(CBI);
 }
 
 void Verifier::visitSelectInst(SelectInst &SI) {
   Assert(!SelectInst::areInvalidOperands(SI.getOperand(0), SI.getOperand(1),
                                          SI.getOperand(2)),
          "Invalid operands for select instruction!", &SI);

llvm/test/Verifier/callbr.ll

+; RUN: not opt -verify -S < %s 2>&1 | FileCheck %s
+
+; CHECK: Did not find indirect destination in callbr operand list
+
+define i32 @test_asm_goto(i32 %x){
+entry:
+  callbr void asm "", "r,X"(i32 %x, i8* blockaddress(@test_asm_goto, %not_in_indirect_list)) to label %fallthrough [label %indirect]
+
+fallthrough:
+  ret i32 1
+indirect:
+  ret i32 0
+not_in_indirect_list:
+  ret i32 2
+}