[LLVMbugs] [Bug 1602] New: Mid-level optimizer doesn't "devirtualize" simple reference

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=1602

           Summary: Mid-level optimizer doesn't "devirtualize" simple
                    reference
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Keywords: code-quality, regression
          Severity: enhancement
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sabre at nondot.org
                CC: llvmbugs at cs.uiuc.edu


On this simple C++ ptr-to-method example, the optimizer gets confused by the
ptrtoint inttoptr stuff:

  struct S { virtual void f(); };
  typedef void (S::*P)(void);
  const P p = &S::f; 
 void g(S s) {
   (s.*p)();
 }

This generates atrocious code like:

define void @_Z1g1S(%struct.S* %s) {
entry:
        br i1 icmp eq (i32 and (i32 ptrtoint (void (%struct.S*)* inttoptr (i64
1 to void (%struct.S*)*) to i32), i32 1), i32 0), label %cond_next, label
%cond_true

This is optimized away at the codegen level, but the mid-level optimizer should
also eliminate this stuff.

-Chris


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