Add loop unswitch pass.

It moves all conditional branching and switch whose conditions are loop
invariant and uniform. Before performing the loop unswitch we check that
the loop does not contain any instruction that would prevent it
(barriers, group instructions etc.).

1 files changed, 6 insertions, 0 deletions

diff --git a/tools/opt/opt.cpp b/tools/opt/opt.cpp
index 3f8dd884..9c9a2710 100644
--- a/tools/opt/opt.cpp
+++ b/tools/opt/opt.cpp
@@ -187,6 +187,10 @@ Options (in lexicographical order):
   --local-redundancy-elimination
                Looks for instructions in the same basic block that compute the
                same value, and deletes the redundant ones.
+  --loop-unswitch
+               Hoists loop-invariant conditionals out of loops by duplicating
+               the loop on each branch of the conditional and adjusting each
+               copy of the loop.
   -O
                Optimize for performance. Apply a sequence of transformations
                in an attempt to improve the performance of the generated
@@ -463,6 +467,8 @@ OptStatus ParseFlags(int argc, const char** argv, Optimizer* optimizer,
         optimizer->RegisterPass(CreateDeadVariableEliminationPass());
       } else if (0 == strcmp(cur_arg, "--fold-spec-const-op-composite")) {
         optimizer->RegisterPass(CreateFoldSpecConstantOpAndCompositePass());
+      } else if (0 == strcmp(cur_arg, "--loop-unswitch")) {
+        optimizer->RegisterPass(CreateLoopUnswitchPass());
       } else if (0 == strcmp(cur_arg, "--scalar-replacement")) {
         optimizer->RegisterPass(CreateScalarReplacementPass());
       } else if (0 == strcmp(cur_arg, "--strength-reduction")) {