[PATCH] D39368: DAG: Add computeKnownBitsForFrameIndex

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
Herald added subscribers: tpr, wdng.

Some of the AMDGPU stack addressing modes require knowing the sign
bit is zero. We used to accomplish this by custom lowering
frame indexes, and then putting an AssertZext around a
TargetFrameIndex. This required specifically looking for
the AssextZext + frame index pattern which was moderately
disgusting. The same could probably be accomplished
with a target specific node, but would still
require special handling of frame indexes.


https://reviews.llvm.org/D39368

Files:
  include/llvm/Target/TargetLowering.h
  lib/CodeGen/SelectionDAG/SelectionDAG.cpp


Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2854,8 +2854,9 @@
     if (unsigned Align = InferPtrAlignment(Op)) {
       // The low bits are known zero if the pointer is aligned.
       Known.Zero.setLowBits(Log2_32(Align));
-      break;
     }
+
+    TLI->computeKnownBitsForFrameIndex(Op, Known, DemandedElts, *this, Depth);
     break;
 
   default:
Index: include/llvm/Target/TargetLowering.h
===================================================================
--- include/llvm/Target/TargetLowering.h
+++ include/llvm/Target/TargetLowering.h
@@ -2678,6 +2678,14 @@
                                              const SelectionDAG &DAG,
                                              unsigned Depth = 0) const;
 
+  virtual void computeKnownBitsForFrameIndex(const SDValue Op,
+                                             KnownBits &Known,
+                                             const APInt &DemandedElts,
+                                             const SelectionDAG &DAG,
+                                             unsigned Depth = 0) const {
+    return;
+  }
+
   /// This method can be implemented by targets that want to expose additional
   /// information about sign bits to the DAG Combiner. The DemandedElts
   /// argument allows us to only collect the minimum sign bits that are shared


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