[llvm-commits] [PATCH] FindPHIForConditionForwarding - switch's case ranges support.

[Stepan Dyatkovskiy]

Hi all. How do you find the extension of FindPHIForConditionForwarding 
for switches with case-ranges.
In current implementation it is supposed that 'switch' contains single 
numbers only.

Consider the code below:

   switch i32 %m, label %sw.bb4 [
     i32 0, label %sw.bb0
     i32 1, label %sw.bb1
   ]
sw.bb0:
   br label %return
sw.bb1:
   br label %return
return:
   %retval = phi i32 [ 1, %sw.bb1 ], [ 0, %sw.bb0 ]

The %retval will simplified by this method to the next one:
%retval = phi i32 [ %m, %sw.bb1 ], [ %m, %sw.bb0 ]

Please review the patch attached, that allows to do something like this 
for switch with case ranges:

Consider the code below (case ranges syntax is still "under construction"):

   switch i32 %m, label %sw.bb4 [
     [<i32 0, i32 5>], label %sw.bb0
     [<i32 20, i32 25>], label %sw.bb1
   ]
sw.bb0:
   br label %return
sw.bb1:
   br label %return
return:
   %retval = phi i32 [ 2, %sw.bb1 ], [ 22, %sw.bb0 ]

Since '2' belongs to [<i32 0, i32 5>] and '22' belongs to [<i32 20, i32 
25>], the %retval will also simplified to the next one:
%retval = phi i32 [ %m, %sw.bb1 ], [ %m, %sw.bb0 ]

-Stepan.
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