[Bug rtl-optimization/17236] inefficient code for long long multiply on x86

[bonzini at gnu dot org]

------- Comment #25 from bonzini at gnu dot org  2007-12-19 13:50 -------
Note that "fwprop" is not an exact term, because there *is* a memory load in
each multiplication, and propagating a second memory operand will create an
invalid insn.  You may try to add a split from reg=op(mem1, mem2) to
reg=mem1;reg=reg*mem2, but anyway, it won't help propagating into the mull,
since it is not LOG_LINKS-related to the load.

The problem is that we end up with having to reload *anyway*.  If we had a way
to express the relationship between operands 0 and 1 of the multiplication
*before reload*, probably the RTL optimizations could do much more.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17236