[Clang] New loop pragma vectorize_predicate

This adds a new vectorize predication loop hint:

  #pragma clang loop vectorize_predicate(enable)

that can be used to indicate to the vectoriser that all (load/store)
instructions should be predicated (masked). This allows, for example, folding
of the remainder loop into the main loop.

This patch will be followed up with D64916 and D65197. The former is a
refactoring in the loopvectorizer and the groundwork to make tail loop folding
a more general concept, and in the latter the actual tail loop folding
transformation will be implemented.

Differential Revision: https://reviews.llvm.org/D64744

llvm-svn: 366989

1 files changed, 10 insertions, 2 deletions

diff --git a/clang/lib/Sema/SemaStmtAttr.cpp b/clang/lib/Sema/SemaStmtAttr.cpp
index 791c52c2d91..e819d96470c 100644
--- a/clang/lib/Sema/SemaStmtAttr.cpp
+++ b/clang/lib/Sema/SemaStmtAttr.cpp
@@ -133,6 +133,7 @@ static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const ParsedAttr &A,
                  .Case("vectorize", LoopHintAttr::Vectorize)
                  .Case("vectorize_width", LoopHintAttr::VectorizeWidth)
                  .Case("interleave", LoopHintAttr::Interleave)
+                 .Case("vectorize_predicate", LoopHintAttr::VectorizePredicate)
                  .Case("interleave_count", LoopHintAttr::InterleaveCount)
                  .Case("unroll", LoopHintAttr::Unroll)
                  .Case("unroll_count", LoopHintAttr::UnrollCount)
@@ -151,6 +152,7 @@ static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const ParsedAttr &A,
       State = LoopHintAttr::Numeric;
     } else if (Option == LoopHintAttr::Vectorize ||
                Option == LoopHintAttr::Interleave ||
+               Option == LoopHintAttr::VectorizePredicate ||
                Option == LoopHintAttr::Unroll ||
                Option == LoopHintAttr::Distribute ||
                Option == LoopHintAttr::PipelineDisabled) {
@@ -189,7 +191,8 @@ CheckForIncompatibleAttributes(Sema &S,
     const LoopHintAttr *StateAttr;
     const LoopHintAttr *NumericAttr;
   } HintAttrs[] = {{nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr},
-                   {nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr}};
+                   {nullptr, nullptr}, {nullptr, nullptr}, {nullptr, nullptr},
+                   {nullptr, nullptr}};
 
   for (const auto *I : Attrs) {
     const LoopHintAttr *LH = dyn_cast<LoopHintAttr>(I);
@@ -205,7 +208,8 @@ CheckForIncompatibleAttributes(Sema &S,
       Unroll,
       UnrollAndJam,
       Distribute,
-      Pipeline
+      Pipeline,
+      VectorizePredicate
     } Category;
     switch (Option) {
     case LoopHintAttr::Vectorize:
@@ -232,6 +236,9 @@ CheckForIncompatibleAttributes(Sema &S,
     case LoopHintAttr::PipelineInitiationInterval:
       Category = Pipeline;
       break;
+    case LoopHintAttr::VectorizePredicate:
+      Category = VectorizePredicate;
+      break;
     };
 
     assert(Category < sizeof(HintAttrs) / sizeof(HintAttrs[0]));
@@ -240,6 +247,7 @@ CheckForIncompatibleAttributes(Sema &S,
     if (Option == LoopHintAttr::Vectorize ||
         Option == LoopHintAttr::Interleave || Option == LoopHintAttr::Unroll ||
         Option == LoopHintAttr::UnrollAndJam ||
+        Option == LoopHintAttr::VectorizePredicate ||
         Option == LoopHintAttr::PipelineDisabled ||
         Option == LoopHintAttr::Distribute) {
       // Enable|Disable|AssumeSafety hint.  For example, vectorize(enable).