[SelectionDAG] Fixed issue with uitofp vector constant folding being treated as sitofp

[RKSimon]

Summary

While the uitofp scalar constant folding treated an integer as an unsigned value (from lang ref):

%X = sitofp i8 -1 to double ; yields double:-1.0
%Y = uitofp i8 -1 to double ; yields double:255.0

The vector constant folding was always using sitofp:

%X = sitofp <2 x i8> <i8 -1, i8 -1> to <2 x double> ; yields <double -1.0, double -1.0>
%Y = uitofp <2 x i8> <i8 -1, i8 -1> to <2 x double> ; yields <double -1.0, double -1.0>

This patch fixes this so that the correct opcode is used for sitofp and uitofp.

%X = sitofp <2 x i8> <i8 -1, i8 -1> to <2 x double> ; yields <double -1.0, double -1.0>
%Y = uitofp <2 x i8> <i8 -1, i8 -1> to <2 x double> ; yields <double 255.0, double 255.0>

[hfinkel]

LGTM.

llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

if (BuildVectorSDNode *BV = dyn_cast<BuildVectorSDNode>(Operand.getNode())) {
     if (BV->isConstant()) {
       switch (Opcode) {
       default:
         // FIXME: Entirely reasonable to perform folding of other unary
         // operations here as the need arises.
         break;
       case ISD::UINT_TO_FP:
       case ISD::SINT_TO_FP: {
+        // Let the above scalar folding handle the folding of each element.
         SmallVector<SDValue, 8> Ops;
         for (int i = 0, e = VT.getVectorNumElements(); i != e; ++i) {
           SDValue OpN = BV->getOperand(i);
-          // Let the above scalar folding handle the conversion of each
-          // element.
-          OpN = getNode(ISD::SINT_TO_FP, DL, VT.getVectorElementType(),
-                        OpN);
+          OpN = getNode(Opcode, DL, VT.getVectorElementType(), OpN);
           Ops.push_back(OpN);
         }
         return getNode(ISD::BUILD_VECTOR, DL, VT, Ops);
       }
       }
     }
   }
 

llvm/trunk/test/CodeGen/X86/x86-setcc-int-to-fp-combine.ll

 ; CHECK: cmpeqps %xmm1, %xmm0
 ; CHECK-NEXT: andps LCPI3_0(%rip), %xmm0
   %cmp = fcmp oeq <4 x float> %val, %test
   %ext = zext <4 x i1> %cmp to <4 x i32>
   %and = and <4 x i32> %ext, <i32 255, i32 256, i32 257, i32 258>
   %result = sitofp <4 x i32> %and to <4 x float>
   ret <4 x float> %result
 }
+
+; Test the general purpose constant folding of uint->fp.
+define void @foo4(<4 x float>* noalias %result) nounwind {
+; CHECK-LABEL: LCPI4_0:
+; CHECK-NEXT: .long 1065353216              ## float 1.000000e+00
+; CHECK-NEXT: .long 1123942400              ## float 1.270000e+02
+; CHECK-NEXT: .long 1124073472              ## float 1.280000e+02
+; CHECK-NEXT: .long 1132396544              ## float 2.550000e+02
+; CHECK-LABEL: foo4:
+; CHECK:  movaps LCPI4_0(%rip), %xmm0
+
+  %val = uitofp <4 x i8> <i8 1, i8 127, i8 -128, i8 -1> to <4 x float>
+  store <4 x float> %val, <4 x float>* %result
+  ret void
+}