Implement negation of longs efficiently. For this testcase:

long %test(long %X) {
        %Y = sub long 0, %X
        ret long %Y
}

We used to generate:

test:
        sub %ESP, 4
        mov DWORD PTR [%ESP], %ESI
        mov %ECX, DWORD PTR [%ESP + 8]
        mov %ESI, DWORD PTR [%ESP + 12]
        mov %EAX, 0
        mov %EDX, 0
        sub %EAX, %ECX
        sbb %EDX, %ESI
        mov %ESI, DWORD PTR [%ESP]
        add %ESP, 4
        ret

Now we generate:

test:
        mov %EAX, DWORD PTR [%ESP + 4]
        mov %EDX, DWORD PTR [%ESP + 8]
        neg %EAX
        adc %EDX, 0
        neg %EDX
        ret

llvm-svn: 12681

1 files changed, 11 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/InstSelectSimple.cpp b/llvm/lib/Target/X86/InstSelectSimple.cpp
index 6144b626a67..d44288678ca 100644
--- a/llvm/lib/Target/X86/InstSelectSimple.cpp
+++ b/llvm/lib/Target/X86/InstSelectSimple.cpp
@@ -1690,14 +1690,23 @@ void ISel::emitSimpleBinaryOperation(MachineBasicBlock *MBB,
   unsigned Class = getClassB(Op0->getType());
 
   // sub 0, X -> neg X
-  if (OperatorClass == 1 && Class != cLong)
+  if (OperatorClass == 1)
     if (ConstantInt *CI = dyn_cast<ConstantInt>(Op0)) {
       if (CI->isNullValue()) {
         unsigned op1Reg = getReg(Op1, MBB, IP);
         static unsigned const NEGTab[] = {
-          X86::NEG8r, X86::NEG16r, X86::NEG32r
+          X86::NEG8r, X86::NEG16r, X86::NEG32r, 0, X86::NEG32r
         };
         BuildMI(*MBB, IP, NEGTab[Class], 1, DestReg).addReg(op1Reg);
+
+        if (Class == cLong) {
+          // We just emitted: Dl = neg Sl
+          // Now emit       : T  = addc Sh, 0
+          //                : Dh = neg T
+          unsigned T = makeAnotherReg(Type::IntTy);
+          BuildMI(*MBB, IP, X86::ADC32ri, 2, T).addReg(op1Reg+1).addImm(0);
+          BuildMI(*MBB, IP, X86::NEG32r, 1, DestReg+1).addReg(T);
+        }
         return;
       }
     } else if (ConstantFP *CFP = dyn_cast<ConstantFP>(Op0))