[GVN] Add support for unary FNeg to GVN pass

[arsenm]

LGTM

llvm/trunk/lib/Transforms/Scalar/GVN.cpp

if (!isa<Instruction>(V)) {
     return nextValueNumber++;
   }
 
   Instruction* I = cast<Instruction>(V);
   Expression exp;
   switch (I->getOpcode()) {
     case Instruction::Call:
       return lookupOrAddCall(cast<CallInst>(I));
+    case Instruction::FNeg:
     case Instruction::Add:
     case Instruction::FAdd:
     case Instruction::Sub:
     case Instruction::FSub:
     case Instruction::Mul:
     case Instruction::FMul:
     case Instruction::UDiv:
     case Instruction::SDiv:

llvm/trunk/test/Transforms/GVN/fpmath.ll

; CHECK: %foo = fadd double %add1, %add1
   %add1 = fadd double %x, %y, !fpmath !0
   %add2 = fadd double %x, %y, !fpmath !1
   %foo = fadd double %add1, %add2
   ret double %foo
 }
 
 define double @test5(double %x, double %y) {
 ; CHECK: @test5(double %x, double %y)
-; CHECK: %neg1 = fneg double %x, !fpmath !0
-; CHECK: %neg2 = fneg double %x, !fpmath !1
-; CHECK: %foo = fadd double %neg1, %neg2
+; CHECK: %neg1 = fneg double %x, !fpmath !1
+; CHECK: %foo = fadd double %neg1, %neg1
   %neg1 = fneg double %x, !fpmath !0
   %neg2 = fneg double %x, !fpmath !1
   %foo = fadd double %neg1, %neg2
   ret double %foo
 }
 
 !0 = !{ float 5.0 }
 !1 = !{ float 2.5 }