[LLVMbugs] [Bug 11202] New: Block addresses can refer to non-existent symbols

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Fri Oct 21 09:43:57 PDT 2011


           Summary: Block addresses can refer to non-existent symbols
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: Pidgeot18 at gmail.com
                CC: llvmbugs at cs.uiuc.edu

This is a minimized test case:
@bb = constant [1 x i8*] [i8* blockaddress(@main, %mid)]
define void @main() {
  br label %l1
  %a = zext i1 0 to i32
  br label %mid
  br label %l2
  %b = zext i1 0 to i32
  br label %l1

If you run this with llc, the output assembly/object file will refuse to
compile with an undefined reference to '.Ltmp3'. Remove any instruction, or
change any branch, and the code will assemble properly.

It seems that the cases where this problem occurs are when an empty basic
1. Has its address taken
2. Is sandwiched between two non-empty basic blocks
3. The outer two basic blocks get optimized into nothing.

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