[LLVMbugs] [Bug 22101] New: At -O2, debug info says variable has constant value

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon Jan 5 18:12:20 PST 2015


            Bug ID: 22101
           Summary: At -O2, debug info says variable has constant value
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: paul_robinson at playstation.sony.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 13636
  --> http://llvm.org/bugs/attachment.cgi?id=13636&action=edit
Sample source

On x86-64 Linux, compiling the attached source with -O2 -g, the debug info
for local variable "compare" has DW_AT_const_value = 0, but actually it can
become 1 or -1.

Trying to reduce the source much further caused the const_value to go away,
leaving "compare" with no location at all, which isn't what I wanted to show.

Might be related to PR22099 but it feels different, mainly because it's
clear "compare" has a fairly extensive lifetime, which is not the case
with the other example.

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