[ubsan] Make the C++ code here not cast floating point values outside the range of an integer type to that integer type.

[chandlerc]

Summary

Instead, change the random value function to cast to the destination
type first and do the devision by 8 afterward. When the destination is
floating point this should be roughly equivalent, but when it is an
integer type it will end up truncating stuff down rather than ending up
outside the range.

[asbirlea]

LGTM. Thanks for the change!

test-suite/trunk/Bitcode/Regression/vector_widen/driver.cpp

 #include "halide_buffer.h"
 
 template<typename T>
 T rand_value() {
-    return (T)(rand() * 0.125) - 100;
+    return (T)((T)rand() / 8) - 100;
 }
 
 template<typename T>
 buffer_t make_buffer(int w, int h) {
     T *mem = new T[w*h];
     buffer_t buf = {0};
     buf.host = (uint8_t *)mem;
     buf.extent[0] = w;

test-suite/trunk/Bitcode/simd_ops/simd_ops.cpp

 #if defined(__aarch64__) || defined(__arm__)
 #define FACTOR 5
 #else
 #define FACTOR 1
 #endif
 
 template<typename T>
 T rand_value() {
-    return (T)(rand() * 0.125) - 100;
+    return (T)((T)rand() / 8) - 100;
 }
 
 // Even on android, we want errors to stdout
 extern "C" void halide_print(void *, const char *msg) {
     printf("%s\n", msg);
 }
 
 template<typename T>