[LLVMdev] GlobalValues appear in their own use lists?

[Sean Callanan]

In the following IR module:
–
define i8 @foo() #0 {
entry:
  %call0 = call i8 @bar()
  ret i8 %call0
}

declare i8 @bar() #1
–
@bar() gets marked as its own user in top-of-tree LLVM.  I patched the Verifier to check it (but didn’t commit the patch):
–
Index: lib/IR/Verifier.cpp
===================================================================
--- lib/IR/Verifier.cpp	(revision 203468)
+++ lib/IR/Verifier.cpp	(working copy)
@@ -360,6 +360,11 @@
           "Global is external, but doesn't have external or weak linkage!",
           &GV);
 
+  for (Value::const_use_iterator UI = GV.use_begin(), UE = GV.use_end();
+       UI != UE; ++UI) {
+    Assert1(*UI != &GV, "Global values cannot be their own uses!", &GV);
+  }
+
   Assert1(!GV.hasAppendingLinkage() || isa<GlobalVariable>(GV),
           "Only global variables can have appending linkage!", &GV);
–
Is it ever reasonable for a global value to be its own use?  If not, can I commit this patch?

This really causes problems for LLDB in various parts of our logic, including infinite loops when following use chains, but a major issue is that we try to strip certain global values out of the module, and if they’re their own uses then that doesn’t work because we can never eliminate the last use.

Sean

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