llvm-diff: add support for diffing the callbr instruction

[void]

Summary

The only wrinkle is that we can't process the "blockaddress" arguments
of the callbr until the blocks have been equated. So we force them to be
"unified" before checking.

This was left out when the callbr instruction was added.

[void]

Rebase with top-of-tree.

[rjmccall]

LGTM

llvm/test/tools/llvm-diff/callbr.ll

+; RUN: not llvm-diff %s %s 2>&1 | FileCheck %s
+
+define void @foo() {
+entry:
+  callbr void asm sideeffect "", "X,X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %return), i8* blockaddress(@foo, %t_no))
+          to label %asm.fallthrough [label %return, label %t_no]
+
+asm.fallthrough:
+  br label %return
+
+t_no:
+  br label %return
+
+return:
+  ret void
+}
+
+; CHECK:      in function bar:
+; CHECK-NOT:  in function foo:
+; CHECK-NEXT:  in block %entry:
+; CHECK-NEXT:    >   callbr void asm sideeffect "", "X,X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %t_no), i8* blockaddress(@foo, %return))
+; CHECK-NEXT:          to label %asm.fallthrough [label %return, label %t_no]
+; CHECK-NEXT:    <   callbr void asm sideeffect "", "X,X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %t_no), i8* blockaddress(@foo, %return))
+; CHECK-NEXT:          to label %asm.fallthrough [label %return, label %t_no]
+
+define void @bar() {
+entry:
+  callbr void asm sideeffect "", "X,X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@foo, %t_no), i8* blockaddress(@foo, %return))
+          to label %asm.fallthrough [label %return, label %t_no]
+
+asm.fallthrough:
+  br label %return
+
+t_no:
+  br label %return
+
+return:
+  ret void
+}

llvm/tools/llvm-diff/DifferenceEngine.cpp

// Terminators.
         return true;
 
       if (TryUnify) {
         tryUnify(LI.getNormalDest(), RI.getNormalDest());
         tryUnify(LI.getUnwindDest(), RI.getUnwindDest());
       }
       return false;
 
+    } else if (isa<CallBrInst>(L)) {
+      const CallBrInst &LI = cast<CallBrInst>(*L);
+      const CallBrInst &RI = cast<CallBrInst>(*R);
+      if (LI.getNumIndirectDests() != RI.getNumIndirectDests()) {
+        if (Complain)
+          Engine.log("callbr # of indirect destinations differ");
+        return true;
+      }
+
+      // Perform the "try unify" step so that we can equate the indirect
+      // destinations before checking the call site.
+      for (unsigned I = 0; I < LI.getNumIndirectDests(); I++)
+        tryUnify(LI.getIndirectDest(I), RI.getIndirectDest(I));
+
+      if (diffCallSites(LI, RI, Complain))
+        return true;
+
+      if (TryUnify)
+        tryUnify(LI.getDefaultDest(), RI.getDefaultDest());
+      return false;
+
     } else if (isa<BranchInst>(L)) {
       const BranchInst *LI = cast<BranchInst>(L);
       const BranchInst *RI = cast<BranchInst>(R);
       if (LI->isConditional() != RI->isConditional()) {
         if (Complain) Engine.log("branch conditionality differs");
         return true;
       }