Add experimental -enable-lsr-phielim option.

I'm not sure we will need it in the long run, but the option is
currently useful for checking if the output of LSR is "clean".

llvm-svn: 141634

1 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 26fc03b18b6..d03b86a7e9d 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -83,6 +83,12 @@ cl::opt<bool> EnableNested(
 
 cl::opt<bool> EnableRetry(
     "enable-lsr-retry", cl::Hidden, cl::desc("Enable LSR retry"));
+
+// Temporary flag to cleanup congruent phis after LSR phi expansion.
+// It's currently disabled until we can determine whether it's truly useful or
+// not. The flag should be removed after the v3.0 release.
+cl::opt<bool> EnablePhiElim(
+    "enable-lsr-phielim", cl::Hidden, cl::desc("Enable LSR phi elimination"));
 }
 
 namespace {
@@ -3816,6 +3822,14 @@ LSRInstance::LSRInstance(const TargetLowering *tli, Loop *l, Pass *P)
 
   // Skip nested loops until we can model them better with formulae.
   if (!EnableNested && !L->empty()) {
+
+    if (EnablePhiElim) {
+      // Remove any extra phis created by processing inner loops.
+      SmallVector<WeakVH, 16> DeadInsts;
+      SCEVExpander Rewriter(SE, "lsr");
+      Changed |= Rewriter.replaceCongruentIVs(L, &DT, DeadInsts);
+      Changed |= DeleteTriviallyDeadInstructions(DeadInsts);
+    }
     DEBUG(dbgs() << "LSR skipping outer loop " << *L << "\n");
     return;
   }
@@ -3861,6 +3875,14 @@ LSRInstance::LSRInstance(const TargetLowering *tli, Loop *l, Pass *P)
 
   // Now that we've decided what we want, make it so.
   ImplementSolution(Solution, P);
+
+  if (EnablePhiElim) {
+    // Remove any extra phis created by processing inner loops.
+    SmallVector<WeakVH, 16> DeadInsts;
+    SCEVExpander Rewriter(SE, "lsr");
+    Changed |= Rewriter.replaceCongruentIVs(L, &DT, DeadInsts);
+    Changed |= DeleteTriviallyDeadInstructions(DeadInsts);
+  }
 }
 
 void LSRInstance::print_factors_and_types(raw_ostream &OS) const {