core.checkedint?

[safety0ff via digitalmars-d-ldc]

I'm not terribly interested in preparing a PR for this, but I 
believe the code should be something like this (untested):

ldc/src/core/checkedint.d:

uint mulu(uint x, uint y, ref bool overflow)
{
+ version (LDC)
+ {
+     auto res = llvm_umul_with_overflow(x, y);
+     overflow |= res.overflow;
+     return res.result;
+ }
+ else
+ {
       ulong r = ulong(x) * ulong(y);
       if (r > uint.max)
           overflow = true;
       return cast(uint)r;
+ }
}

Rinse and repeat with:
llvm_uadd_with_overflow, llvm_sadd_with_overflow, 
llvm_usub_with_overflow, llvm_ssub_with_overflow, 
llvm_smul_with_overflow.