[Bug tree-optimization/105596] Loop counter widened to 128-bit unnecessarily

[peter at cordes dot ca]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105596

--- Comment #1 from Peter Cordes <peter at cordes dot ca> ---
https://godbolt.org/z/aoG55T5Yq
gcc -O3 -m32 has the same problem with  unsigned long long total  and unsigned
i.

Pretty much identical instruction sequences in the loop for all 3 versions,
doing add/adc to increment i, for example.  (Plus a bit of spilling). 
fact_gcc_handhold still compiles without the unnecessary widening.

Perhaps should retitle to widen to a "2-register type".

IDK how easily this occurs in real-world loops with 64 and 32-bit integers on
32-bit machines, but that's probably more of a concern for wasting more clock
cycles worldwide.