http://llvm.org/bugs/show_bug.cgi?id=8108
Summary: Missed optimization opportunity with duplicated
conditional (JumpThreading?)
Product: libraries
Version: trunk
Platform: PC
OS/Version: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
See the attached .ll files. In particular, note this snippet:
lor.rhs.i:
%cmp9.i = icmp eq i32 %tmp2, 16
br label %_Z16sparc_floating_pPK4type.exit
_Z16sparc_floating_pPK4type.exit:
%call19 = phi i1 [ true, %sw.bb.i ], [ %cmp9.i, %lor.rhs.i ], [ true,
%sw.bb.i ]
%cmp = icmp eq i32 %tmp2, 16
%or.cond = and i1 %call19, %cmp
br i1 %or.cond, label %if.end18, label %sw.bb.i24
Notice that the comparison of %tmp2 with 16 is repeated. If this edge were to
be threaded by JumpThreading, GVN would pick up the duplication and get rid of
it. However, because we can't actually determine a *value* for the comparison
JumpThreading does not currently choose to thread this edge.
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