[ARM][TypePromotion] Enable by default

Enable the TypePromotion pass my default (again).

This patch was originally committed in 393dacacf7e7.
This patch was reverted in a38396939c54.

Differential Revision: https://reviews.llvm.org/D70998

1 files changed, 21 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/TypePromotion.cpp b/llvm/lib/CodeGen/TypePromotion.cpp
index d78589c4a05..000cd366dd6 100644
--- a/llvm/lib/CodeGen/TypePromotion.cpp
+++ b/llvm/lib/CodeGen/TypePromotion.cpp
@@ -46,7 +46,7 @@
 using namespace llvm;
 
 static cl::opt<bool>
-DisablePromotion("disable-type-promotion", cl::Hidden, cl::init(true),
+DisablePromotion("disable-type-promotion", cl::Hidden, cl::init(false),
                  cl::desc("Disable type promotion pass"));
 
 // The goal of this pass is to enable more efficient code generation for
@@ -902,16 +902,34 @@ bool TypePromotion::TryToPromote(Value *V, unsigned PromotedWidth) {
              for (auto *I : CurrentVisited)
                I->dump();
              );
+
+  // Check that promoting this at the IR level is most likely beneficial. It's
+  // more likely if we're operating over multiple blocks and handling wrapping
+  // instructions.
   unsigned ToPromote = 0;
+  unsigned NonFreeArgs = 0;
+  SmallPtrSet<BasicBlock*, 4> Blocks;
   for (auto *V : CurrentVisited) {
-    if (Sources.count(V))
+    if (auto *I = dyn_cast<Instruction>(V))
+      Blocks.insert(I->getParent());
+
+    if (Sources.count(V)) {
+      if (auto *Arg = dyn_cast<Argument>(V)) {
+        if (!Arg->hasZExtAttr() && !Arg->hasSExtAttr())
+          ++NonFreeArgs;
+      }
       continue;
+    }
+
     if (Sinks.count(cast<Instruction>(V)))
       continue;
+
     ++ToPromote;
   }
 
-  if (ToPromote < 2)
+  // DAG optimisations should be able to handle these cases better, especially
+  // for function arguments.
+  if (ToPromote < 2 || (Blocks.size() == 1 && (NonFreeArgs > SafeWrap.size())))
     return false;
 
   Promoter->Mutate(OrigTy, PromotedWidth, CurrentVisited, Sources, Sinks,