[Review]: Fix Integer Division Expansion special case of divide by 1

[Aditya Nandakumar]

Hi All

I think the handling of special case of divide by 1 is incorrect in udivsi3.c (compiler-rt) and it’s equivalent in llvm/lib/Transforms/Utils/IntegerDivision.cpp

I think we want to check if the clz(divisor) == (Num_word_bits - 1) rather than checking
(clz(divisor) - clz(dividend)) == (Num_word_bits - 1)

I also think compiler-rt should be updated - 
http://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/builtins/udivsi3.c <http://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/builtins/udivsi3.c>

sr = __builtin_clz(d) - __builtin_clz(n);
    /* 0 <= sr <= n_uword_bits - 1 or sr large */
    if (sr > n_uword_bits - 1)  /* d > r */
        return 0;
    if (sr == n_uword_bits - 1)  /* d == 1 */
        return n;
The last line should be replaced with 
	
	if ( __buildin_clz(d) == n_uword_bits - 1)
		return n;

I have attached the LLVM patch here for the same.


Thanks
Aditya
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