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

[Chris Lattner]

Changes in directory llvm/lib/CodeGen/SelectionDAG:

SelectionDAG.cpp updated: 1.15 -> 1.16
---
Log message:

Add a simple transformation.  This allows us to compile one of the inner 
loops in stepanov to this:

.LBB_Z5test0PdS__2:     # no_exit.1
        fldl data(,%eax,8)
        fldl 24(%esp)
        faddp %st(1)
        fstl 24(%esp)
        incl %eax
        cmpl $2000, %eax
        fstpl 16(%esp)
        #FP_REG_KILL
        jl .LBB_Z5test0PdS__2

instead of this:

.LBB_Z5test0PdS__2:     # no_exit.1
        fldl data(,%eax,8)
        fldl 24(%esp)
        faddp %st(1)
        fstl 24(%esp)
        incl %eax
        movl $data, %ecx
        movl %ecx, %edx
        addl $16000, %edx
        subl %ecx, %edx
        movl %edx, %ecx
        sarl $2, %ecx
        shrl $29, %ecx
        addl %ecx, %edx
        sarl $3, %edx
        cmpl %edx, %eax
        fstpl 16(%esp)
        #FP_REG_KILL
        jl .LBB_Z5test0PdS__2

The old instruction selector produced:

.LBB_Z5test0PdS__2:     # no_exit.1
        fldl 24(%esp)
        faddl data(,%eax,8)
        fstl 24(%esp)
        movl %eax, %ecx
        incl %ecx
        incl %eax
        leal data+16000, %edx
        movl $data, %edi
        subl %edi, %edx
        movl %edx, %edi
        sarl $2, %edi
        shrl $29, %edi
        addl %edi, %edx
        sarl $3, %edx
        cmpl %edx, %ecx
        fstpl 16(%esp)
        #FP_REG_KILL
        jl .LBB_Z5test0PdS__2   # no_exit.1

Which is even worse!



---
Diffs of the changes:  (+8 -0)

Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1.15 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1.16
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:1.15	Sat Jan  8 02:08:56 2005
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp	Sun Jan  9 14:09:57 2005
@@ -662,6 +662,14 @@
   case ISD::XOR:
     if (N1 == N2) return getConstant(0, VT);  // xor X, Y -> 0
     break;
+  case ISD::SUB:
+    if (N1.getOpcode() == ISD::ADD) {
+      if (N1.Val->getOperand(0) == N2)
+        return N1.Val->getOperand(1);         // (A+B)-A == B
+      if (N1.Val->getOperand(1) == N2)
+        return N1.Val->getOperand(0);         // (A+B)-B == A
+    }
+    break;
   }
 
   SDNode *&N = BinaryOps[std::make_pair(Opcode, std::make_pair(N1, N2))];