[LLVMdev] How to eliminate PHI nodes on pointer types?

[Andrew Clinton]

Somewhere during optimization PHI nodes on pointer types (including 
alloca instructions) are being introduced, and they persist through the 
scalar replacement of aggregates pass and others.  I can't seem to find 
a combination of passes or transformations to get rid of them.  Has 
anyone had this problem before, and know a transformation to eliminate 
it?  My optimization passes rely on everything being in pure SSA form.

One more note, this particular optimization problem only seems to occur 
in llvm 2.8, not 3.0 - though I can't say for sure whether it never 
happens in 3.0.

Here's an example from the compiled code:


define private void @"vop_bindST at FFIFFI"(double* %news, double* %ss, 
i32* %isSConnected, double* %newt, double* %tt, i32* %isTConnected) 
nounwind alwaysinline {
entry:
   %"reg2mem alloca point" = bitcast i32 0 to i32
   %isSConnected1 = load i32* %isSConnected
   %0 = icmp eq i32 %isSConnected1, 0
   br i1 %0, label %false, label %true

true:                                             ; preds = %entry
   br label %end

false:                                            ; preds = %entry
   br label %end

end:                                              ; preds = %false, %true
   %phi.in.reg2mem.0 = phi double* [ @s, %false ], [ %ss, %true ]
   %phi = load double* %phi.in.reg2mem.0
   store double %phi, double* %news
   %isTConnected4 = load i32* %isTConnected
   %1 = icmp eq i32 %isTConnected4, 0
   br i1 %1, label %false6, label %true5

true5:                                            ; preds = %end
   br label %end7

false6:                                           ; preds = %end
   br label %end7

end7:                                             ; preds = %false6, %true5
   %phi9.in.reg2mem.0 = phi double* [ @t, %false6 ], [ %tt, %true5 ]
   %phi9 = load double* %phi9.in.reg2mem.0
   store double %phi9, double* %newt
   ret void
}