[LoopVectorize] Convert scalable vectorization optimization remark to LLVM_DEBUG

[MaskRay]

Summary

After D98509,
clang --target=x86_64-linux-gnu -O2 -Rpass-analysis=loop-analysis may emit the remark,

a.cc:6:3: remark: Disabling scalable vectorization, because target does not support scalable vectors. [-Rpass-analysis]
  for (int i = 0; i < 128; i++)
  ^
a.cc:6:3: remark: vectorized loop (vectorization width: 4, interleaved count: 2) [-Rpass=loop-vectorize]

which is inappropriate for targets which don't support scalable vectorization.
Arguably it is also inappropriate on AArch64 when SVE is disabled.

LLVM_DEBUG should be sufficient.
I simplify the remark and use the preferred style
https://llvm.org/docs/CodingStandards.html#error-and-warning-messages

[fhahn]

Alternatively we could issue a positive remark when scalable vectorization is enabled?

[paulwalker-arm]

As a counter can I offer D108028 as I'd prefer to maintain a remark for the situation where a user has specifically requested scalable vectorisation via a hint. The patch also fixes what looks like a bug in the expected output for one of the tests.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

bool LoopVectorizationCostModel::runtimeChecksRequired() {
   }
 
   return false;
 }
 
 ElementCount
 LoopVectorizationCostModel::getMaxLegalScalableVF(unsigned MaxSafeElements) {
   if (!TTI.supportsScalableVectors() && !ForceTargetSupportsScalableVectors) {
-    reportVectorizationInfo(
-        "Disabling scalable vectorization, because target does not "
-        "support scalable vectors.",
-        "ScalableVectorsUnsupported", ORE, TheLoop);
+    LLVM_DEBUG(
+        dbgs() << "LV: disable scalable vectorization which is unsupported\n");
     return ElementCount::getScalable(0);
   }
 
   if (Hints->isScalableVectorizationDisabled()) {
     reportVectorizationInfo("Scalable vectorization is explicitly disabled",
                             "ScalableVectorizationDisabled", ORE, TheLoop);
     return ElementCount::getScalable(0);
   }

llvm/test/Transforms/LoopVectorize/AArch64/scalable-vf-hint.ll

exit:
   ret void
 }
 
 !15 = !{!15, !16, !17}
 !16 = !{!"llvm.loop.vectorize.width", i32 16}
 !17 = !{!"llvm.loop.vectorize.scalable.enable", i1 true}
 
 ; CHECK-NO-SVE-REMARKS-LABEL: LV: Checking a loop in "test_no_sve"
-; CHECK-NO-SVE-REMARKS: LV: Disabling scalable vectorization, because target does not support scalable vectors.
-; CHECK-NO-SVE-REMARKS: remark: <unknown>:0:0: Disabling scalable vectorization, because target does not support scalable vectors.
+; CHECK-NO-SVE-REMARKS: LV: disable scalable vectorization which is unsupported
 ; CHECK-NO-SVE-REMARKS: LV: User VF=vscale x 4 is unsafe. Ignoring scalable UserVF.
 ; CHECK-NO-SVE-REMARKS: LV: Selecting VF: 4.
 ; CHECK-NO-SVE-LABEL: @test_no_sve
 ; CHECK-NO-SVE: <4 x i32>
 ; CHECK-NO-SVE-NOT: <vscale x 4 x i32>
 define void @test_no_sve(i32* %a, i32* %b) {
 entry:
   br label %loop

llvm/test/Transforms/LoopVectorize/scalable-vf-hint.ll

 ; REQUIRES: asserts
 ; RUN: opt -loop-vectorize -pass-remarks-analysis=loop-vectorize -debug-only=loop-vectorize -S -scalable-vectorization=on < %s 2>&1 | FileCheck %s
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
-; CHECK: LV: Disabling scalable vectorization, because target does not support scalable vectors.
-; CHECK: remark: <unknown>:0:0: Disabling scalable vectorization, because target does not support scalable vectors.
+; CHECK: LV: disable scalable vectorization which is unsupported
 ; CHECK: LV: The Widest register safe to use is: 32 bits.
 define void @test1(i32* %a, i32* %b) {
 entry:
   br label %loop
 
 loop:
   %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
   %arrayidx = getelementptr inbounds i32, i32* %a, i64 %iv