[llvm] [LV] Fix emission of debug message in legality check (PR #101924)

[Madhur Amilkanthwar via llvm-commits]

https://github.com/madhur13490 created https://github.com/llvm/llvm-project/pull/101924

Successful vectorization message is emitted even
after "Result" is false.  "Result" = false indicates failure of one of the legality check and thus
successful message should not be printed.

>From 6782629300d8e25bab09a588b4650c569c9c642e Mon Sep 17 00:00:00 2001
From: Madhur Amilkanthwar <madhura at nvidia.com>
Date: Wed, 31 Jul 2024 22:17:56 +0530
Subject: [PATCH] [LV] Fix emission of debug message in legality check

Successful vectorization message is emitted even
after "Result" is false.  "Result" = false indicates
failure of one of the legality check and thus
successful message should not be printed.
---
 .../Vectorize/LoopVectorizationLegality.cpp    | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 465d0df30e3f7..35c841f470261 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -1441,10 +1441,12 @@ bool LoopVectorizationLegality::canVectorize(bool UseVPlanNativePath) {
   // Check whether the loop-related control flow in the loop nest is expected by
   // vectorizer.
   if (!canVectorizeLoopNestCFG(TheLoop, UseVPlanNativePath)) {
-    if (DoExtraAnalysis)
+    if (DoExtraAnalysis) {
+      LLVM_DEBUG(dbgs() << "LV legality check failed: loop nest");
       Result = false;
-    else
+    } else {
       return false;
+    }
   }
 
   // We need to have a loop header.
@@ -1509,11 +1511,6 @@ bool LoopVectorizationLegality::canVectorize(bool UseVPlanNativePath) {
       return false;
   }
 
-  LLVM_DEBUG(dbgs() << "LV: We can vectorize this loop"
-                    << (LAI->getRuntimePointerChecking()->Need
-                            ? " (with a runtime bound check)"
-                            : "")
-                    << "!\n");
 
   unsigned SCEVThreshold = VectorizeSCEVCheckThreshold;
   if (Hints->getForce() == LoopVectorizeHints::FK_Enabled)
@@ -1528,6 +1525,13 @@ bool LoopVectorizationLegality::canVectorize(bool UseVPlanNativePath) {
     else
       return false;
   }
+  if (Result) {
+    LLVM_DEBUG(dbgs() << "LV: We can vectorize this loop"
+                      << (LAI->getRuntimePointerChecking()->Need
+                            ? " (with a runtime bound check)"
+                            : "")
+                      << "!\n");
+  }
 
   // Okay! We've done all the tests. If any have failed, return false. Otherwise
   // we can vectorize, and at this point we don't have any other mem analysis