[llvm] [LV] Emit better debug and opt-report messages when vectorization is disallowed in the LoopVectorizer (PR #158513)

[Florian Hahn via llvm-commits]

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@@ -182,14 +182,40 @@ void LoopVectorizeHints::setAlreadyVectorized() {
 bool LoopVectorizeHints::allowVectorization(
     Function *F, Loop *L, bool VectorizeOnlyWhenForced) const {
   if (getForce() == LoopVectorizeHints::FK_Disabled) {
-    LLVM_DEBUG(dbgs() << "LV: Not vectorizing: #pragma vectorize disable.\n");
-    emitRemarkWithHints();
+    if (Force.Value == LoopVectorizeHints::FK_Disabled) {
+      LLVM_DEBUG(dbgs() << "LV: Not vectorizing: #pragma vectorize disable.\n");
+      ORE.emit(OptimizationRemarkMissed(LV_NAME, "MissedExplicitlyDisabled",
+                                        TheLoop->getStartLoc(),
+                                        TheLoop->getHeader())
+               << "loop not vectorized: vectorization is explicitly disabled");
+    } else if (hasDisableAllTransformsHint(TheLoop)) {
+      LLVM_DEBUG(
+          dbgs() << "LV: Not vectorizing: loop hasDisableAllTransformsHint.\n");
+      ORE.emit(OptimizationRemarkMissed(LV_NAME, "MissedTransformsDisabled",
+                                        TheLoop->getStartLoc(),
+                                        TheLoop->getHeader())
+               << "loop not vectorized: loop transformations are disabled");
+    } else {
+      // This should be unreachable unless there is a bug.
+      LLVM_DEBUG(dbgs() << "LV: [BUG] Not vectorizing: loop vect disabled for "
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fhahn wrote:

In LLVM, it is common to use `llvm_unreachable`, if not, better to drop `[BUG]`

https://github.com/llvm/llvm-project/pull/158513