[llvm-commits] CVS: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

[Chris Lattner]

Changes in directory llvm/lib/CodeGen/SelectionDAG:

SelectionDAG.cpp updated: 1.118 -> 1.119
---
Log message:

Add some simplifications for MULH[SU].  This allows us to compile this:

long %bar(long %X) {
  %Y = mul long %X, 4294967297
  ret long %Y
}

to this:

l1_bar:
        mov %EAX, DWORD PTR [%ESP + 4]
        mov %EDX, %EAX
        add %EDX, DWORD PTR [%ESP + 8]
        ret

instead of:

l1_bar:
        mov %ECX, DWORD PTR [%ESP + 4]
        mov %EDX, 1
        mov %EAX, %ECX
        mul %EDX
        add %EDX, %ECX
        add %EDX, DWORD PTR [%ESP + 8]
        mov %EAX, %ECX
        ret



---
Diffs of the changes:  (+12 -0)

 SelectionDAG.cpp |   12 ++++++++++++
 1 files changed, 12 insertions(+)


Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1.118 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1.119
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1.118	Sat May 14 02:45:46 2005
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp	Sun May 15 00:39:08 2005
@@ -843,6 +843,8 @@
   case ISD::XOR:
   case ISD::UDIV:
   case ISD::UREM:
+  case ISD::MULHU:
+  case ISD::MULHS:
     assert(MVT::isInteger(VT) && "This operator does not apply to FP types!");
     // fall through
   case ISD::ADD:
@@ -941,6 +943,16 @@
       }
       break;
 
+    case ISD::MULHU:
+    case ISD::MULHS:
+      if (!C2) return N2;         // mul X, 0 -> 0
+
+      if (C2 == 1)                // 0X*01 -> 0X  hi(0X) == 0
+        return getConstant(0, VT);
+
+      // Many others could be handled here, including -1, powers of 2, etc.
+      break;
+
     case ISD::UDIV:
       // FIXME: Move this to the DAG combiner when it exists.
       if ((C2 & C2-1) == 0 && C2) {