rootn: Use denormal path only

It's OK to either flush to 0 or return denormal result if the device
does not support denormals. See sec 7.2 and 7.5.3 of OCL specs
Use 0.0f explicitly intead of relying on GPU to flush it.
Fixes CTS on carrizo and turks

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Acked-by: Aaron Watry <awatry@gmail.com>
Tested-by: Aaron Watry <awatry@gmail.com>

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@332324 91177308-0d34-0410-b5e6-96231b3b80d8

generic/lib/math/clc_rootn.cl

@@ -170,16 +170,7 @@ _CLC_DEF _CLC_OVERLOAD float __clc_rootn(float x, int ny)
     tv = USE_TABLE(exp_tbl_ep, j);
 
     float expylogx = mad(tv.s0, poly, mad(tv.s1, poly, tv.s1)) + tv.s0;
-    float sexpylogx;
-    if (!__clc_fp32_subnormals_supported()) {
-		int explg = ((as_uint(expylogx) & EXPBITS_SP32 >> 23) - 127);
-		m = (23-(m + 149)) == 0 ? 1: m;
-		uint mantissa =  ((as_uint(expylogx) & MANTBITS_SP32)|IMPBIT_SP32) >> (23-(m + 149));
-		sexpylogx = as_float(mantissa);
-    } else {
-		sexpylogx = expylogx * as_float(0x1 << (m + 149));
-    }
-
+    float sexpylogx = __clc_fp32_subnormals_supported() ? expylogx * as_float(0x1 << (m + 149)) : 0.0f;
 
     float texpylogx = as_float(as_int(expylogx) + m2);
     expylogx = m < -125 ? sexpylogx : texpylogx;