[Clang] Ensure vector predication loop metadata is always emitted when pragma is specified.

This patch ensures that vector predication and vectorization width
pragmas work together correctly/as expected. Specifically, this patch
fixes the issue that when vectorization_width > 1, the vector
predication behaviour (this would matter if it has NOT been disabled
explicitly by a pragma) was getting ignored, which was incorrect.

The fix here removes the dependence of vector predication on the
vectorization width. The loop metadata corresponding to clang loop
pragma vectorize_predicate is always emitted, if the pragma is
specified, even if vectorization is disabled by vectorize_width(1)
or vectorize(disable) since the option is also used for interleaving
by the LoopVectorize pass.

Reviewed By: dmgreen, Meinersbur

Differential Revision: https://reviews.llvm.org/D94779

Author: malJaj

clang/lib/CodeGen/CGLoopInfo.cpp

@@ -250,12 +250,10 @@ LoopInfo::createLoopVectorizeMetadata(const LoopAttributes &Attrs,
   Args.push_back(nullptr);
   Args.append(LoopProperties.begin(), LoopProperties.end());
 
-  // Setting vectorize.predicate
+  // Setting vectorize.predicate when it has been specified and vectorization
+  // has not been disabled.
   bool IsVectorPredicateEnabled = false;
-  if (Attrs.VectorizePredicateEnable != LoopAttributes::Unspecified &&
-      Attrs.VectorizeEnable != LoopAttributes::Disable &&
-      Attrs.VectorizeWidth < 1) {
-
+  if (Attrs.VectorizePredicateEnable != LoopAttributes::Unspecified) {
     IsVectorPredicateEnabled =
         (Attrs.VectorizePredicateEnable == LoopAttributes::Enable);
 
@@ -303,7 +301,8 @@ LoopInfo::createLoopVectorizeMetadata(const LoopAttributes &Attrs,
   //    explicitly requested fixed-width vectorization, i.e.
   //    vectorize.scalable.enable is false.
   if (Attrs.VectorizeEnable != LoopAttributes::Unspecified ||
-      IsVectorPredicateEnabled || Attrs.VectorizeWidth > 1 ||
+      (IsVectorPredicateEnabled && Attrs.VectorizeWidth != 1) ||
+      Attrs.VectorizeWidth > 1 ||
       Attrs.VectorizeScalable == LoopAttributes::Enable ||
       (Attrs.VectorizeScalable == LoopAttributes::Disable &&
        Attrs.VectorizeWidth != 1)) {

clang/test/CodeGenCXX/pragma-loop-predicate.cpp

@@ -58,6 +58,49 @@ void test5(int *List, int Length) {
     List[i] = i * 2;
 }
 
+// Check that vectorize_predicate is ignored when vectorization width is 1
+void test6(int *List, int Length) {
+// CHECK-LABEL: @{{.*}}test6{{.*}}(
+// CHECK: br label {{.*}}, !llvm.loop ![[LOOP6:.*]]
+
+#pragma clang loop vectorize_predicate(disable) vectorize_width(1)
+  for (int i = 0; i < Length; i++)
+    List[i] = i * 2;
+}
+
+
+// Check that vectorize_width(!=1) does not affect vectorize_predicate.
+void test7(int *List, int Length) {
+// CHECK-LABEL: @{{.*}}test7{{.*}}(
+// CHECK: br label {{.*}}, !llvm.loop ![[LOOP7:.*]]
+
+#pragma clang loop vectorize_predicate(disable) vectorize_width(4)
+  for (int i = 0; i < Length; i++)
+    List[i] = i * 2;
+}
+
+
+// Check that vectorize_predicate is ignored when vectorization width is 1
+void test8(int *List, int Length) {
+// CHECK-LABEL: @{{.*}}test8{{.*}}(
+// CHECK: br label {{.*}}, !llvm.loop ![[LOOP8:.*]]
+
+#pragma clang loop vectorize_predicate(enable) vectorize_width(1)
+  for (int i = 0; i < Length; i++)
+    List[i] = i * 2;
+}
+
+
+// Check that vectorize_width(!=1) does not affect vectorize_predicate.
+void test9(int *List, int Length) {
+// CHECK-LABEL: @{{.*}}test9{{.*}}(
+// CHECK: br label {{.*}}, !llvm.loop ![[LOOP9:.*]]
+
+#pragma clang loop vectorize_predicate(enable) vectorize_width(4)
+  for (int i = 0; i < Length; i++)
+    List[i] = i * 2;
+}
+
 // CHECK:      ![[LOOP0]] = distinct !{![[LOOP0]], [[MP:![0-9]+]], [[GEN3:![0-9]+]]}
 // CHECK:      [[MP]] = !{!"llvm.loop.mustprogress"}
 // CHECK-NEXT: [[GEN3]] = !{!"llvm.loop.vectorize.enable", i1 true}
@@ -73,4 +116,14 @@ void test5(int *List, int Length) {
 // CHECK-NEXT: ![[LOOP4]] = distinct !{![[LOOP4]], [[MP]], [[GEN10:![0-9]+]]}
 // CHECK-NEXT: [[GEN10]] = !{!"llvm.loop.vectorize.width", i32 1}
 
-// CHECK-NEXT: ![[LOOP5]] = distinct !{![[LOOP5]], [[MP]], [[GEN10]]}
+// CHECK-NEXT: ![[LOOP5]] = distinct !{![[LOOP5]], [[MP]], [[GEN6]], [[GEN10]]}
+
+// CHECK-NEXT: ![[LOOP6]] = distinct !{![[LOOP6]], [[MP]], [[GEN8]], [[GEN10]], [[GEN11:![0-9]+]]}
+// CHECK-NEXT: [[GEN11]] = !{!"llvm.loop.vectorize.scalable.enable", i1 false}
+
+// CHECK-NEXT: ![[LOOP7]] = distinct !{![[LOOP7]], [[MP]], [[GEN8]], [[GEN12:![0-9]+]], [[GEN11]], [[GEN3]]}
+// CHECK-NEXT: [[GEN12]] = !{!"llvm.loop.vectorize.width", i32 4}
+
+// CHECK-NEXT: ![[LOOP8]] = distinct !{![[LOOP8]], [[MP]], [[GEN6]], [[GEN10]], [[GEN11]]}
+
+// CHECK-NEXT: ![[LOOP9]] = distinct !{![[LOOP9]], [[MP]], [[GEN6]], [[GEN12]], [[GEN11]], [[GEN3]]}