#61: Darwin+clang doesn't produce a working lisp --------------------+------------------------------------------------------- Reporter: rtoy | Owner: somebody Type: defect | Status: new Priority: major | Milestone: Component: Core | Version: 2012-07 Keywords: | --------------------+------------------------------------------------------- Compiling the C runtime on Darwin with clang does not produce a working lisp. The cause is that clang uses xmm registers in gencgc.c, but the allocator calls {{{alloc()}}} directly without saving any live xmm registers which eventually get trashed. For example the vop {{{ (define-vop (move-from-single) (:args (x :scs (single-reg) :to :save)) (:results (y :scs (descriptor-reg))) (:node-var node) (:note _N"float to pointer coercion") (:save-p t) (:generator 13 (with-fixed-allocation (y vm:single-float-type vm:single-float-size node) (inst movss (ea-for-sf-desc y) x)))) }}} will save any live float registers, but not the arg {{{x}}}. If the allocator calls {{{alloc()}}}, {{{x}}} could be destroyed. Possible solutions: 1. Save and restore float args to the stack in every float vop that does allocation. 1. Make {{{alloc()}}} save all the float registers. The first solution is nice because only the registers that need to be saved are saved. But it's not nice because every vop will save/restore when most of the time {{{alloc()}}} will not be called. The second solution is nice because it's always safe, even if some vop forgot to save a register. But it's not nice because all float registers are saved when only one (or a very small number) needs to be saved. But it looks like {{{alloc()}}} is relatively expensive so perhaps the cost of saving all registers is in the noise. (Should measure this.) -- Ticket URL: <http://trac.common-lisp.net/cmucl/ticket/61> cmucl <http://common-lisp.net/project/cmucl> Cmucl is a high-performance, free Common Lisp implementation.