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Simon Marlow authored
We occasionally need to reserve some temporary memory in a primop for passing to a foreign function. We've been using the stack for this, but when we moved to high-level Cmm it became quite fragile because primops are in high-level Cmm and the stack is supposed to be under the control of the Cmm pipeline. So this change puts things on a firmer footing by adding a new Cmm construct 'reserve'. e.g. in decodeFloat_Int#: reserve 2 = tmp { mp_tmp1 = tmp + WDS(1); mp_tmp_w = tmp; /* Perform the operation */ ccall __decodeFloat_Int(mp_tmp1 "ptr", mp_tmp_w "ptr", arg); r1 = W_[mp_tmp1]; r2 = W_[mp_tmp_w]; } reserve is described in CmmParse.y. Unfortunately the argument to reserve must be a compile-time constant. We might have to extend the parser to allow expressions with arithmetic operators if this is too restrictive. Note also that the return instruction for the procedure must be outside the scope of the reserved stack area, so we have to extract the values from the reserved area before we close the scope. This means some more local variables (r1, r2 in the example above). The generated code is more or less identical to what we had before though.
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