[LV] Tail-Loop Folding

This allows folding of the scalar epilogue loop (the tail) into the main
vectorised loop body when the loop is annotated with a "vector predicate"
metadata hint. To fold the tail, instructions need to be predicated (masked),
enabling/disabling lanes for the remainder iterations.

Differential Revision: https://reviews.llvm.org/D65197

llvm-svn: 367592

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 6ef8dc2d3cd..cede505aed2 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -88,6 +88,7 @@ bool LoopVectorizeHints::Hint::validate(unsigned Val) {
   case HK_FORCE:
     return (Val <= 1);
   case HK_ISVECTORIZED:
+  case HK_PREDICATE:
     return (Val == 0 || Val == 1);
   }
   return false;
@@ -99,7 +100,9 @@ LoopVectorizeHints::LoopVectorizeHints(const Loop *L,
     : Width("vectorize.width", VectorizerParams::VectorizationFactor, HK_WIDTH),
       Interleave("interleave.count", InterleaveOnlyWhenForced, HK_UNROLL),
       Force("vectorize.enable", FK_Undefined, HK_FORCE),
-      IsVectorized("isvectorized", 0, HK_ISVECTORIZED), TheLoop(L), ORE(ORE) {
+      IsVectorized("isvectorized", 0, HK_ISVECTORIZED),
+      Predicate("vectorize.predicate.enable", 0, HK_PREDICATE), TheLoop(L),
+      ORE(ORE) {
   // Populate values with existing loop metadata.
   getHintsFromMetadata();
 
@@ -250,7 +253,7 @@ void LoopVectorizeHints::setHint(StringRef Name, Metadata *Arg) {
     return;
   unsigned Val = C->getZExtValue();
 
-  Hint *Hints[] = {&Width, &Interleave, &Force, &IsVectorized};
+  Hint *Hints[] = {&Width, &Interleave, &Force, &IsVectorized, &Predicate};
   for (auto H : Hints) {
     if (Name == H->Name) {
       if (H->validate(Val))