[llvm-commits] [LLVM, loop-unswitch, bugfix for #11429] Wrong behaviour for switches.

[Stepan Dyatkovskiy]

Hi all. Please find the patch in attachment for review. Regression tests 
are attached in separated patch.

Short tests description:

2011-11-18-SimpleSwitch.ll
Check simple that simple switch will totally unswitched:

for (...)
   switch(c) {
     case 0: inc(); break;
     case 1: dec(); break;
     default: goto loop_exit;
   }

loop_exit:
...

Result of processing should be 2 additional loops for c == 0 and for c == 1.


2011-11-18-TwoSwitches.ll
Check that second switch will unswitched too. Check that switches will 
not unswitched again in new loop:

Initially we have the next:

for (...) {
   switch(c) {
     case 0: inc(); break;
   }
   switch(d) {
     case 0: inc(); break;
   }
}

After optimization we should got 3 additional loops: when (c == 0 && d 
== 0), when (c == 0 && d != 0) and when (c != 0 && d == 0). Original 
loop will activated for (c != 0 && d != 0):

if (c == 0 && d == 0) {
   for (...) ... // All is clear here. Two "switch(0)" instructions.
} else if (c == 0 && d != 0) {
   for (...) {
     switch (0) { // c == 0
       case 0: inc(); break;
     }
     switch (d) {
       case 0: goto unreachable; // CHECK: That it will not unswitched
                         // again, since it looks "trivial",
                         // see LoopUnswitch::IsTrivialUnswitchCondition
     }
   }
} else if (c != 0 && d == 0) {
   // the same...
   ...
} else { // if (c != 0 && d != 0)
   // Original totally unswitched loop:
   switch (c) {
     case 0: goto unreachable;
   }
   switch (d) {
     case 0: goto unreachable;
   }
}

Stepan.
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