Revert r372082 "[Clang] Pragma vectorize_width() implies vectorize(enable)"

This broke the Chromium build. Consider the following code:

  float ScaleSumSamples_C(const float* src, float* dst, float scale, int width) {
    float fsum = 0.f;
    int i;
  #if defined(__clang__)
  #pragma clang loop vectorize_width(4)
  #endif
    for (i = 0; i < width; ++i) {
      float v = *src++;
      fsum += v * v;
      *dst++ = v * scale;
    }
    return fsum;
  }

Compiling at -Oz, Clang  now warns:

  $ clang++ -target x86_64 -Oz -c /tmp/a.cc
  /tmp/a.cc:1:7: warning: loop not vectorized: the optimizer was unable to
  perform the requested transformation; the transformation might be disabled or
  specified as part of an unsupported transformation ordering
  [-Wpass-failed=transform-warning]

this suggests it's not actually enabling vectorization hard enough.

At -Os it asserts instead:

  $ build.release/bin/clang++ -target x86_64 -Os -c /tmp/a.cc
  clang-10: /work/llvm.monorepo/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:2734: void
  llvm::InnerLoopVectorizer::emitMemRuntimeChecks(llvm::Loop*, llvm::BasicBlock*): Assertion `
  !BB->getParent()->hasOptSize() && "Cannot emit memory checks when optimizing for size"' failed.

Of course neither of these are what the developer expected from the pragma.

> Specifying the vectorization width was supposed to implicitly enable
> vectorization, except that it wasn't really doing this. It was only
> setting the vectorize.width metadata, but not vectorize.enable.
>
> This should fix PR27643.
>
> Differential Revision: https://reviews.llvm.org/D66290

llvm-svn: 372225

clang/lib/CodeGen/CGLoopInfo.cpp

@@ -270,14 +270,6 @@ LoopInfo::createLoopVectorizeMetadata(const LoopAttributes &Attrs,
 
   // Setting vectorize.width
   if (Attrs.VectorizeWidth > 0) {
-    // This implies vectorize.enable = true, but only add it when it is not
-    // already enabled.
-    if (Attrs.VectorizeEnable != LoopAttributes::Enable)
-      Args.push_back(
-          MDNode::get(Ctx, {MDString::get(Ctx, "llvm.loop.vectorize.enable"),
-                            ConstantAsMetadata::get(ConstantInt::get(
-                                llvm::Type::getInt1Ty(Ctx), 1))}));
-
     Metadata *Vals[] = {
         MDString::get(Ctx, "llvm.loop.vectorize.width"),
         ConstantAsMetadata::get(ConstantInt::get(llvm::Type::getInt32Ty(Ctx),

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

@@ -58,6 +58,7 @@ void test5(int *List, int Length) {
     List[i] = i * 2;
 }
 
+
 // CHECK:      ![[LOOP0]] = distinct !{![[LOOP0]], !3}
 // CHECK-NEXT: !3 = !{!"llvm.loop.vectorize.enable", i1 true}
 
@@ -69,7 +70,7 @@ void test5(int *List, int Length) {
 
 // CHECK-NEXT: ![[LOOP3]] = distinct !{![[LOOP3]], !5, !3}
 
-// CHECK-NEXT: ![[LOOP4]] = distinct !{![[LOOP4]], !3, !10}
+// CHECK-NEXT: ![[LOOP4]] = distinct !{![[LOOP4]], !10}
 // CHECK-NEXT: !10 = !{!"llvm.loop.vectorize.width", i32 1}
 
-// CHECK-NEXT: ![[LOOP5]] = distinct !{![[LOOP5]], !3, !10}
+// CHECK-NEXT: ![[LOOP5]] = distinct !{![[LOOP5]], !10}

clang/test/CodeGenCXX/pragma-loop.cpp

@@ -158,41 +158,23 @@ void template_test(double *List, int Length) {
   for_template_constant_expression_test<double, 2, 4, 8>(List, Length);
 }
 
-void vec_width_1(int *List, int Length) {
-// CHECK-LABEL: @{{.*}}vec_width_1{{.*}}(
-// CHECK: br label {{.*}}, !llvm.loop ![[LOOP_15:.*]]
-
-  #pragma clang loop vectorize(enable) vectorize_width(1)
-  for (int i = 0; i < Length; i++)
-    List[i] = i * 2;
-}
-
-void width_1(int *List, int Length) {
-// CHECK-LABEL: @{{.*}}width_1{{.*}}(
-// CHECK: br label {{.*}}, !llvm.loop ![[LOOP_16:.*]]
-
-  #pragma clang loop vectorize_width(1)
-  for (int i = 0; i < Length; i++)
-    List[i] = i * 2;
-}
-
 // CHECK: ![[LOOP_1]] = distinct !{![[LOOP_1]], ![[UNROLL_FULL:.*]]}
 // CHECK: ![[UNROLL_FULL]] = !{!"llvm.loop.unroll.full"}
 
-// CHECK: ![[LOOP_2]] = distinct !{![[LOOP_2]], ![[UNROLL_DISABLE:.*]], ![[DISTRIBUTE_DISABLE:.*]], ![[VECTORIZE_ENABLE:.*]], ![[WIDTH_8:.*]], ![[INTERLEAVE_4:.*]]}
+// CHECK: ![[LOOP_2]] = distinct !{![[LOOP_2]], ![[UNROLL_DISABLE:.*]], ![[DISTRIBUTE_DISABLE:.*]], ![[WIDTH_8:.*]], ![[INTERLEAVE_4:.*]]}
 // CHECK: ![[UNROLL_DISABLE]] = !{!"llvm.loop.unroll.disable"}
 // CHECK: ![[DISTRIBUTE_DISABLE]] = !{!"llvm.loop.distribute.enable", i1 false}
-// CHECK: ![[VECTORIZE_ENABLE]] = !{!"llvm.loop.vectorize.enable", i1 true}
 // CHECK: ![[WIDTH_8]] = !{!"llvm.loop.vectorize.width", i32 8}
 // CHECK: ![[INTERLEAVE_4]] = !{!"llvm.loop.interleave.count", i32 4}
 
-// CHECK: ![[LOOP_3]] = distinct !{![[LOOP_3]], ![[INTERLEAVE_4:.*]], ![[VECTORIZE_ENABLE]], ![[FOLLOWUP_VECTOR_3:.*]]}
+// CHECK: ![[LOOP_3]] = distinct !{![[LOOP_3]], ![[INTERLEAVE_4:.*]], ![[INTENABLE_1:.*]], ![[FOLLOWUP_VECTOR_3:.*]]}
+// CHECK: ![[INTENABLE_1]] = !{!"llvm.loop.vectorize.enable", i1 true}
 // CHECK: ![[FOLLOWUP_VECTOR_3]] = !{!"llvm.loop.vectorize.followup_all", ![[AFTER_VECTOR_3:.*]]}
 // CHECK: ![[AFTER_VECTOR_3]] = distinct !{![[AFTER_VECTOR_3]], ![[ISVECTORIZED:.*]], ![[UNROLL_8:.*]]}
 // CHECK: ![[ISVECTORIZED]] = !{!"llvm.loop.isvectorized"}
 // CHECK: ![[UNROLL_8]] = !{!"llvm.loop.unroll.count", i32 8}
 
-// CHECK: ![[LOOP_4]] = distinct !{![[LOOP_4]], ![[VECTORIZE_ENABLE]], ![[WIDTH_2:.*]], ![[INTERLEAVE_2:.*]]}
+// CHECK: ![[LOOP_4]] = distinct !{![[LOOP_4]], ![[WIDTH_2:.*]], ![[INTERLEAVE_2:.*]]}
 // CHECK: ![[WIDTH_2]] = !{!"llvm.loop.vectorize.width", i32 2}
 // CHECK: ![[INTERLEAVE_2]] = !{!"llvm.loop.interleave.count", i32 2}
 
@@ -203,7 +185,7 @@ void width_1(int *List, int Length) {
 // CHECK: ![[FOLLOWUP_VECTOR_6]] = !{!"llvm.loop.vectorize.followup_all", ![[AFTER_VECTOR_6:.*]]}
 // CHECK: ![[AFTER_VECTOR_6]] = distinct !{![[AFTER_VECTOR_6]], ![[ISVECTORIZED:.*]], ![[UNROLL_8:.*]]}
 
-// CHECK: ![[LOOP_7]] = distinct !{![[LOOP_7]], ![[VECTORIZE_ENABLE]], ![[WIDTH_5:.*]]}
+// CHECK: ![[LOOP_7]] = distinct !{![[LOOP_7]], ![[WIDTH_5:.*]]}
 // CHECK: ![[WIDTH_5]] = !{!"llvm.loop.vectorize.width", i32 5}
 
 // CHECK: ![[LOOP_8]] = distinct !{![[LOOP_8]], ![[WIDTH_5:.*]]}
@@ -231,9 +213,5 @@ void width_1(int *List, int Length) {
 // CHECK: ![[AFTER_VECTOR_13]] = distinct !{![[AFTER_VECTOR_13]], ![[ISVECTORIZED:.*]], ![[UNROLL_32:.*]]}
 // CHECK: ![[UNROLL_32]] = !{!"llvm.loop.unroll.count", i32 32}
 
-// CHECK: ![[LOOP_14]] = distinct !{![[LOOP_14]], ![[VECTORIZE_ENABLE]], ![[WIDTH_10:.*]]}
+// CHECK: ![[LOOP_14]] = distinct !{![[LOOP_14]], ![[WIDTH_10:.*]]}
 // CHECK: ![[WIDTH_10]] = !{!"llvm.loop.vectorize.width", i32 10}
-
-// CHECK:      ![[LOOP_15]] = distinct !{![[LOOP_15]], ![[WIDTH_1]], ![[VECTORIZE_ENABLE]]}
-
-// CHECK-NEXT: ![[LOOP_16]] = distinct !{![[LOOP_16]], ![[VECTORIZE_ENABLE]], ![[WIDTH_1]]}