Ignore dbg intrinsics in loop-reroll

[weimingz]

Summary

Currently, we get different code with and without -g. This patch marks debug inst and a few other LLVM intrinsics as ignorable for loop-reroll

[vsk]

Is it possible to add a test for this? E.g something that would force the debug message to be printed without your patch.

[weimingz]

added test case

[weimingz]

In D13150#253180, @vsk wrote:

Is it possible to add a test for this? E.g something that would force the debug message to be printed without your patch.

Sure. Please review patch set 2.

[hfinkel]

Please upload this patch with full context (http://llvm.org/docs/Phabricator.html#requesting-a-review-via-the-web-interface).

lib/Transforms/Scalar/LoopRerollPass.cpp

1007

Why these and not others? I suspect that we could get:

case Intrinsic::annotation:
case Intrinsic::ptr_annotation:
case Intrinsic::var_annotation:

and also:

case Intrinsic::invariant_start:
case Intrinsic::invariant_end:
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:

but for these, at least, we'll need test cases because getting them wrong will miscompile code, and also, they're normally associated with bitcasts to get the pointer type right and you'd need to deal with those too.

[weimingz]

adds ptr_annotation, val_annotation. Not sure if we should add lifetime_start/end, invariant_start/end, so I put them under TODO

[weimingz]

lib/Transforms/Scalar/LoopRerollPass.cpp

1007

I added those annotations into white list. I'm not very sure about the rest. I will try to see if I can get some test case

[hfinkel]

LGTM.

lib/Transforms/Scalar/LoopRerollPass.cpp

   return false;
 }
 
+static bool isIgnorableInst(const Instruction *I) {
+  if (isa<DbgInfoIntrinsic>(I))
+    return true;
+  const IntrinsicInst* II = dyn_cast<IntrinsicInst>(I);
+  if (!II)
+    return false;
+  switch (II->getIntrinsicID()) {
+    default:
+      return false;
+    case llvm::Intrinsic::annotation:
+    case llvm::Intrinsic::lifetime_start:
+    case llvm::Intrinsic::lifetime_end:
+      return true;
+  }
+  return false;
+}
+
 bool LoopReroll::DAGRootTracker::validate(ReductionTracker &Reductions) {
   // We now need to check for equivalence of the use graph of each root with
   // that of the primary induction variable (excluding the roots). Our goal

   // Make sure all instructions in the loop are in one and only one
   // set.
   for (auto &KV : Uses) {
-    if (KV.second.count() != 1) {
+    if (KV.second.count() != 1 && !isIgnorableInst(KV.first)) {
       DEBUG(dbgs() << "LRR: Aborting - instruction is not used in 1 iteration: "
             << *KV.first << " (#uses=" << KV.second.count() << ")\n");
       return false;