Set flag default to false, add TODO

Author: lukel97

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -394,7 +394,7 @@ static cl::opt<bool> EnableEarlyExitVectorization(
         "Enable vectorization of early exit loops with uncountable exits."));
 
 static cl::opt<bool> ConsiderRegPressure(
-    "vectorizer-consider-reg-pressure", cl::init(true), cl::Hidden,
+    "vectorizer-consider-reg-pressure", cl::init(false), cl::Hidden,
     cl::desc("Discard VFs if their register pressure is too high."));
 
 // Likelyhood of bypassing the vectorized loop because there are zero trips left
@@ -3700,6 +3700,8 @@ bool LoopVectorizationCostModel::shouldConsiderRegPressureForVF(
   if (ConsiderRegPressure.getNumOccurrences())
     return ConsiderRegPressure;
 
+  // TODO: We should eventually consider register pressure for all targets. The
+  // TTI hook is temporary whilst target-specific issues are being fixed.
   if (TTI.shouldConsiderVectorizationRegPressure())
     return true;