[clang][CodeGen] Fix metadata when vectorization is disabled by pragma (#135163)

Currently, when specifying `vectorize(disable) unroll_count(8)`, the
generated metadata appears as follows:

```
!loop0 = !{!"loop0", !vectorize_width, !followup}
!vectorize_width = !{!"llvm.loop.vectorize.width", i32 1}
!followup = !{!"llvm.loop.vectorize.followup_all", !unroll}
!unroll = !{!"llvm.loop.unroll_count", i32 8}
```

Since the metadata `!vectorize_width` implies that the vectorization is
disabled, the vectorization process is skipped, and the `!followup`
metadata is not processed correctly.

This patch addresses the issue by directly appending properties to the
metadata node when vectorization is disabled, instead of creating a new
follow-up MDNode. In the above case, the generated metadata will now
look like this:

```
!loop0 = !{!"loop0", !vectorize_width, !vectorize_width, !unroll}
!vectorize_width = !{!"llvm.loop.vectorize.width", i32 1}
!unroll = !{!"llvm.loop.unroll_count", i32 8}
```

Author: kasuga-fj

clang/lib/CodeGen/CGLoopInfo.cpp

@@ -221,18 +221,6 @@ LoopInfo::createLoopVectorizeMetadata(const LoopAttributes &Attrs,
     return createUnrollAndJamMetadata(Attrs, LoopProperties, HasUserTransforms);
   }
 
-  // Apply all loop properties to the vectorized loop.
-  SmallVector<Metadata *, 4> FollowupLoopProperties;
-  FollowupLoopProperties.append(LoopProperties.begin(), LoopProperties.end());
-
-  // Don't vectorize an already vectorized loop.
-  FollowupLoopProperties.push_back(
-      MDNode::get(Ctx, MDString::get(Ctx, "llvm.loop.isvectorized")));
-
-  bool FollowupHasTransforms = false;
-  SmallVector<Metadata *, 4> Followup = createUnrollAndJamMetadata(
-      Attrs, FollowupLoopProperties, FollowupHasTransforms);
-
   SmallVector<Metadata *, 4> Args;
   Args.append(LoopProperties.begin(), LoopProperties.end());
 
@@ -286,22 +274,46 @@ LoopInfo::createLoopVectorizeMetadata(const LoopAttributes &Attrs,
   // 5) it is implied when vectorize.width is unset (0) and the user
   //    explicitly requested fixed-width vectorization, i.e.
   //    vectorize.scalable.enable is false.
+  bool VectorizeEnabled = false;
   if (Attrs.VectorizeEnable != LoopAttributes::Unspecified ||
       (IsVectorPredicateEnabled && Attrs.VectorizeWidth != 1) ||
       Attrs.VectorizeWidth > 1 ||
       Attrs.VectorizeScalable == LoopAttributes::Enable ||
       (Attrs.VectorizeScalable == LoopAttributes::Disable &&
        Attrs.VectorizeWidth != 1)) {
-    bool AttrVal = Attrs.VectorizeEnable != LoopAttributes::Disable;
+    VectorizeEnabled = Attrs.VectorizeEnable != LoopAttributes::Disable;
     Args.push_back(
         MDNode::get(Ctx, {MDString::get(Ctx, "llvm.loop.vectorize.enable"),
                           ConstantAsMetadata::get(ConstantInt::get(
-                              llvm::Type::getInt1Ty(Ctx), AttrVal))}));
+                              llvm::Type::getInt1Ty(Ctx), VectorizeEnabled))}));
   }
 
-  if (FollowupHasTransforms)
-    Args.push_back(
-        createFollowupMetadata("llvm.loop.vectorize.followup_all", Followup));
+  // Apply all loop properties to the vectorized loop.
+  SmallVector<Metadata *, 4> FollowupLoopProperties;
+
+  // If vectorization is not explicitly enabled, the follow-up metadata will be
+  // directly appended to the list currently being created. In that case, adding
+  // LoopProperties to FollowupLoopProperties would result in duplication.
+  if (VectorizeEnabled)
+    FollowupLoopProperties.append(LoopProperties.begin(), LoopProperties.end());
+
+  // Don't vectorize an already vectorized loop.
+  FollowupLoopProperties.push_back(
+      MDNode::get(Ctx, MDString::get(Ctx, "llvm.loop.isvectorized")));
+
+  bool FollowupHasTransforms = false;
+  SmallVector<Metadata *, 4> Followup = createUnrollAndJamMetadata(
+      Attrs, FollowupLoopProperties, FollowupHasTransforms);
+
+  if (FollowupHasTransforms) {
+    // If vectorization is explicitly enabled, we create a follow-up metadata,
+    // otherwise directly add the contents of it to Args.
+    if (VectorizeEnabled)
+      Args.push_back(
+          createFollowupMetadata("llvm.loop.vectorize.followup_all", Followup));
+    else
+      Args.append(Followup.begin(), Followup.end());
+  }
 
   HasUserTransforms = true;
   return Args;

clang/test/CodeGenCXX/pragma-loop.cpp

@@ -203,6 +203,43 @@ void for_test_scalable_1(int *List, int Length) {
   }
 }
 
+// Verify for loop is not performing vectorization
+void for_test_width_1(int *List, int Length) {
+#pragma clang loop vectorize_width(1) interleave_count(4) unroll(disable) distribute(disable)
+  for (int i = 0; i < Length; i++) {
+    // CHECK: br label {{.*}}, !llvm.loop ![[LOOP_20:.*]]
+    List[i] = i * 2;
+  }
+}
+
+// Verify for loop is not performing vectorization
+void for_test_fixed_1(int *List, int Length) {
+#pragma clang loop vectorize_width(1, fixed) interleave_count(4) unroll(disable) distribute(disable)
+  for (int i = 0; i < Length; i++) {
+    // CHECK: br label {{.*}}, !llvm.loop ![[LOOP_21:.*]]
+    List[i] = i * 2;
+  }
+}
+
+
+// Verify unroll attributes are directly attached to the loop metadata
+void for_test_vectorize_disable_unroll(int *List, int Length) {
+#pragma clang loop vectorize(disable) unroll_count(8)
+  for (int i = 0; i < Length; i++) {
+    // CHECK: br label {{.*}}, !llvm.loop ![[LOOP_22:.*]]
+    List[i] = i * 2;
+  }
+}
+
+// Verify unroll attributes are directly attached to the loop metadata
+void for_test_interleave_vectorize_disable_unroll(int *List, int Length) {
+#pragma clang loop vectorize(disable) interleave_count(4) unroll_count(8)
+  for (int i = 0; i < Length; i++) {
+    // CHECK: br label {{.*}}, !llvm.loop ![[LOOP_23:.*]]
+    List[i] = i * 2;
+  }
+}
+
 // CHECK-DAG: ![[MP:[0-9]+]] = !{!"llvm.loop.mustprogress"}
 
 // CHECK-DAG: ![[UNROLL_DISABLE:[0-9]+]] = !{!"llvm.loop.unroll.disable"}
@@ -270,3 +307,7 @@ void for_test_scalable_1(int *List, int Length) {
 // CHECK-DAG: ![[LOOP_17]] = distinct !{![[LOOP_17]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[FIXED_VEC]], ![[INTERLEAVE_4]], ![[VECTORIZE_ENABLE]]}
 // CHECK-DAG: ![[LOOP_18]] = distinct !{![[LOOP_18]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[SCALABLE_VEC]], ![[INTERLEAVE_4]], ![[VECTORIZE_ENABLE]]}
 // CHECK-DAG: ![[LOOP_19]] = distinct !{![[LOOP_19]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[WIDTH_1]], ![[SCALABLE_VEC]], ![[INTERLEAVE_4]], ![[VECTORIZE_ENABLE]]}
+// CHECK-DAG: ![[LOOP_20]] = distinct !{![[LOOP_20]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[WIDTH_1]], ![[FIXED_VEC]], ![[INTERLEAVE_4]]}
+// CHECK-DAG: ![[LOOP_21]] = distinct !{![[LOOP_21]], ![[MP]], ![[UNROLL_DISABLE]], ![[DISTRIBUTE_DISABLE]], ![[WIDTH_1]], ![[FIXED_VEC]], ![[INTERLEAVE_4]]}
+// CHECK-DAG: ![[LOOP_22]] = distinct !{![[LOOP_22]], ![[MP]], ![[WIDTH_1]], ![[ISVECTORIZED]], ![[UNROLL_8]]}
+// CHECK-DAG: ![[LOOP_23]] = distinct !{![[LOOP_23]], ![[MP]], ![[WIDTH_1]], ![[INTERLEAVE_4]], ![[ISVECTORIZED]], ![[UNROLL_8]]}