Hi Kavon,
I looked a bit and it does not appear that there is an SSE sqrt in the
native code gen. It should be easy to add (see a similar addition here:
https://phabricator.haskell.org/D3265). The x87 version was available for
32-bit. I think if you use the LLVM backend it will give you the SSE sqrt.
Ryan
On Fri, Apr 28, 2017 at 9:27 AM, Kavon Farvardin
Given a Cmm expression such as
(_c8Gq::F64) = call MO_F64_Sqrt(_s8oX::F64); // CmmUnsafeForeignCall
the native code generator produces an actual call to the sqrt C function, which has the side-effect of causing all floating-point registers to be dumped as they are caller-saved. In the nbody benchmark, this is particularly bad for a rather hot piece of code (see below).
Ideally the NCG would recognize this foreign call and instead use the `sqrtsd` SSE instruction when targeting x86-64.
Does anyone know if the NCG can produce this instruction? I think it would be beneficial, as the below would turn into one or two instructions.
Other math functions such as sin/cos require x87 FPU instructions, which as far as I know we're not using.
;;;;;;;;;;; ; NCG generates this in parts of the nbody benchmark ; to compute the sqrt ; subq $8,%rsp movsd %xmm9,176(%rsp) ; all floating-point registers movsd %xmm1,184(%rsp) ; are caller-saved in SysV ABI movsd %xmm2,192(%rsp) movsd %xmm3,200(%rsp) movq %rdi,208(%rsp) movq %rcx,216(%rsp) movq %rsi,224(%rsp) movsd %xmm4,232(%rsp) movsd %xmm5,240(%rsp) movsd %xmm6,248(%rsp) movsd %xmm7,256(%rsp) movsd %xmm8,264(%rsp) movsd %xmm11,272(%rsp) call _sqrt ;; the loads ;; below are interleaved ;; with computations addq $8,%rsp movsd 264(%rsp),%xmm1 movsd 240(%rsp),%xmm2 movsd 224(%rsp),%xmm2 movsd 232(%rsp),%xmm4 movq 200(%rsp),%rax movsd 248(%rsp),%xmm4 movsd 256(%rsp),%xmm4 movq 216(%rsp),%rcx movsd 192(%rsp),%xmm2
~kavon
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