[PATCH] D103323: [DAGCombiner] Add support for mulhi const folding in DAGCombiner

[David Stuttard via Phabricator via llvm-commits]

dstuttard updated this revision to Diff 348550.
dstuttard added a comment.

Thanks for reviews.
Made suggested changes.

I'll add some test cases as well - but I'm off for a few days. I'll do it on return.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D103323/new/

https://reviews.llvm.org/D103323

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp


Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -5085,6 +5085,18 @@
     if (!C2.getBoolValue())
       break;
     return C1.srem(C2);
+  case ISD::MULHS: {
+    unsigned FullWidth = C1.getBitWidth() * 2;
+    APInt C1Ext = C1.sext(FullWidth);
+    APInt C2Ext = C2.sext(FullWidth);
+    return (C1Ext * C2Ext).extractBits(C1.getBitWidth(), C1.getBitWidth());
+  }
+  case ISD::MULHU: {
+    unsigned FullWidth = C1.getBitWidth() * 2;
+    APInt C1Ext = C1.zext(FullWidth);
+    APInt C2Ext = C2.zext(FullWidth);
+    return (C1Ext * C2Ext).extractBits(C1.getBitWidth(), C1.getBitWidth());
+  }
   }
   return llvm::None;
 }
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4450,6 +4450,11 @@
       return DAG.getConstant(0, DL, VT);
   }
 
+  // fold (mulhs c1, c2)
+  if (SDValue C =
+          DAG.FoldConstantArithmetic(ISD::MULHS, SDLoc(N), VT, {N0, N1}))
+    return C;
+
   // fold (mulhs x, 0) -> 0
   if (isNullConstant(N1))
     return N1;
@@ -4498,6 +4503,11 @@
       return DAG.getConstant(0, DL, VT);
   }
 
+  // fold (mulhu c1, c2)
+  if (SDValue C =
+          DAG.FoldConstantArithmetic(ISD::MULHU, SDLoc(N), VT, {N0, N1}))
+    return C;
+
   // fold (mulhu x, 0) -> 0
   if (isNullConstant(N1))
     return N1;


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