`@floatToInt` now has safety-checked undefined behavior

when the integer part does not fit in the destination integer type

 * Also fix incorrect safety triggered for integer casting an
   `i32` to a `u7`. closes #1138
 * adds compiler-rt function: `__floatuntidf`

1 files changed, 39 insertions, 0 deletions

diff --git a/test/runtime_safety.zig b/test/runtime_safety.zig
index ea5beafe8d..a7e8d6dc0e 100644
--- a/test/runtime_safety.zig
+++ b/test/runtime_safety.zig
@@ -1,6 +1,45 @@
 const tests = @import("tests.zig");
 
 pub fn addCases(cases: *tests.CompareOutputContext) void {
+    cases.addRuntimeSafety("@floatToInt cannot fit - negative to unsigned",
+        \\pub fn panic(message: []const u8, stack_trace: ?*@import("builtin").StackTrace) noreturn {
+        \\    @import("std").os.exit(126);
+        \\}
+        \\pub fn main() void {
+        \\    baz(bar(-1.1));
+        \\}
+        \\fn bar(a: f32) u8 {
+        \\    return @floatToInt(u8, a);
+        \\}
+        \\fn baz(a: u8) void { }
+    );
+
+    cases.addRuntimeSafety("@floatToInt cannot fit - negative out of range",
+        \\pub fn panic(message: []const u8, stack_trace: ?*@import("builtin").StackTrace) noreturn {
+        \\    @import("std").os.exit(126);
+        \\}
+        \\pub fn main() void {
+        \\    baz(bar(-129.1));
+        \\}
+        \\fn bar(a: f32) i8 {
+        \\    return @floatToInt(i8, a);
+        \\}
+        \\fn baz(a: i8) void { }
+    );
+
+    cases.addRuntimeSafety("@floatToInt cannot fit - positive out of range",
+        \\pub fn panic(message: []const u8, stack_trace: ?*@import("builtin").StackTrace) noreturn {
+        \\    @import("std").os.exit(126);
+        \\}
+        \\pub fn main() void {
+        \\    baz(bar(256.2));
+        \\}
+        \\fn bar(a: f32) u8 {
+        \\    return @floatToInt(u8, a);
+        \\}
+        \\fn baz(a: u8) void { }
+    );
+
     cases.addRuntimeSafety("calling panic",
         \\pub fn panic(message: []const u8, stack_trace: ?*@import("builtin").StackTrace) noreturn {
         \\    @import("std").os.exit(126);