Sign-extending 32-bit operands in adapters [Was: [aarch64-port-dev ] RFR: 8129426: aarch64: add support for PopCount in C2]

Andrew Haley aph at
Mon Jun 29 12:15:21 UTC 2015

Here's a snippet from gen_i2c_adapter where we sign extend:

      if (!r_2->is_valid()) {
        // sign extend???
        __ ldrsw(rscratch2, Address(esp, ld_off));
        __ str(rscratch2, Address(sp, st_off));

but in another place we don't sign extend:

        // sign extend and use a full word?
        __ ldrw(r, Address(esp, ld_off));

So, we sign extend when our argument is passed to compiled code in
memory, but zero extend when it is passed in a register.  The
confusion (and those comments) about what should happen seems to come
from the x86 code.  I think we've agreed that we should zero extend,
but I'm still far from convinced that we should ever use an input
operand in any mode other than its natural size.


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