https://bugs.kde.org/show_bug.cgi?id=352364
--- Comment #3 from Julian Seward <jsew...@acm.org> ---
In this example, "cmpld ; bne" translates to essentially this
// the cmpld
t54 = 64to8(CmpORD64U(t48,0xCD:I64))
// the bne
if (CmpEQ32(Xor32(And32(8Uto32(t54),0x2:I32),0x2:I32),0x0:I32))
{ PUT(1296) = 0x100003C4:I64; exit-Boring }
CmpORD64U produces a value that is either 8, 4 or 2, with 8 meaning
"<", 4 meaning ">" and 2 meaning "=". The bne translation then
inspects t54 bit 1 (intel encoding) (hence the use of 0x2). This
completely obscures the fact that what we really want is simply
if (CmpNE64(t48,0xCD:I64) { PUT(1296) = 0x100003C4:I64; exit-Boring }
The tricky part is to change the generated IR so that it directly
exposes the condition on which the branch is based, yet make it
possible for later instructions to recover a correct value for CR0
.. CR7 should they wish to. Maybe we should change the ppc front end
to use a thunk-based representation as most of the other front ends
do, since that does more or less facilitate all of the above.
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