[LLVMbugs] [Bug 13112] New: Phi elimination generates uninitialized vreg uses

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=13112

             Bug #: 13112
           Summary: Phi elimination generates uninitialized vreg uses
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: atrick at apple.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Input to phielim:
v0 = ImplicitDef
v1 = phi(v0, v2)
v2 = X
= v1

Output:
v0 = copy v2
v2 = X
= v0

Since X is the only definition of v2, the DAG builder assumes it dominates its
uses, which is not true for uninitialized uses. To fix this properly,
phielimination needs to preserve joint dominance of vreg uses. Without this
property, we are also unable to recompute liveness after phielim.

I'll disable the DAG builder's SSA check until phielim is fixed.

I'll attach a real test case as soon as I have time.

-- 
Configure bugmail: http://llvm.org/bugs/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.