Added a test for gather/load of textures of 16-bit types. (#1689)

Fixes #739

tools/clang/test/CodeGenHLSL/quick-test/texture_16bittypes.hlsl

@@ -0,0 +1,27 @@
+// RUN: %dxc -E main -T ps_6_2 -enable-16bit-types %s
+
+Texture2D<half> tex_f16;
+Texture2D<int16_t> tex_i16;
+SamplerState samp;
+SamplerComparisonState sampcmp;
+float cmpval;
+
+float isHalf(float); // Overload resolution shouldn't pick this
+float isHalf(half) { return 0; }
+float isInt16(int); // Overload resolution shouldn't pick this
+float isInt16(int16_t) { return 0; }
+
+float main() : SV_Target
+{
+  return isHalf(tex_f16.Gather(samp, 0).x) + isInt16(tex_i16.Gather(samp, 0).x)
+    + isHalf(tex_f16.GatherRed(samp, 0).x) + isInt16(tex_i16.GatherRed(samp, 0).x)
+    + isHalf(tex_f16.GatherGreen(samp, 0).x) + isInt16(tex_i16.GatherGreen(samp, 0).x)
+    + isHalf(tex_f16.GatherBlue(samp, 0).x) + isInt16(tex_i16.GatherBlue(samp, 0).x)
+    + isHalf(tex_f16.GatherAlpha(samp, 0).x) + isInt16(tex_i16.GatherAlpha(samp, 0).x)
+    + isHalf(tex_f16.GatherCmp(sampcmp, 0, cmpval).x) + isInt16(tex_i16.GatherCmp(sampcmp, 0, cmpval).x)
+    + isHalf(tex_f16.GatherCmpRed(sampcmp, 0, cmpval).x) + isInt16(tex_i16.GatherCmpRed(sampcmp, 0, cmpval).x)
+    + isHalf(tex_f16.GatherCmpGreen(sampcmp, 0, cmpval).x) + isInt16(tex_i16.GatherCmpGreen(sampcmp, 0, cmpval).x)
+    + isHalf(tex_f16.GatherCmpBlue(sampcmp, 0, cmpval).x) + isInt16(tex_i16.GatherCmpBlue(sampcmp, 0, cmpval).x)
+    + isHalf(tex_f16.GatherCmpAlpha(sampcmp, 0, cmpval).x) + isInt16(tex_i16.GatherCmpAlpha(sampcmp, 0, cmpval).x)
+    + isHalf(tex_f16.Load(0).x) + isInt16(tex_i16.Load(0).x);
+}