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// Random ideas for the X86 backend: FP stack related stuff
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Some targets (e.g. athlons) prefer freep to fstp ST(0):
http://gcc.gnu.org/ml/gcc-patches/2004-04/msg00659.html
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This should use fiadd on chips where it is profitable:
double foo(double P, int *I) { return P+*I; }
We have fiadd patterns now but the followings have the same cost and
complexity. We need a way to specify the later is more profitable.
def FpADD32m : FpI<(ops RFP:$dst, RFP:$src1, f32mem:$src2), OneArgFPRW,
[(set RFP:$dst, (fadd RFP:$src1,
(extloadf64f32 addr:$src2)))]>;
// ST(0) = ST(0) + [mem32]
def FpIADD32m : FpI<(ops RFP:$dst, RFP:$src1, i32mem:$src2), OneArgFPRW,
[(set RFP:$dst, (fadd RFP:$src1,
(X86fild addr:$src2, i32)))]>;
// ST(0) = ST(0) + [mem32int]
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The FP stackifier should handle simple permutates to reduce number of shuffle
instructions, e.g. turning:
fld P -> fld Q
fld Q fld P
fxch
or:
fxch -> fucomi
fucomi jl X
jg X
Ideas:
http://gcc.gnu.org/ml/gcc-patches/2004-11/msg02410.html
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Add a target specific hook to DAG combiner to handle SINT_TO_FP and
FP_TO_SINT when the source operand is already in memory.
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Open code rint,floor,ceil,trunc:
http://gcc.gnu.org/ml/gcc-patches/2004-08/msg02006.html
http://gcc.gnu.org/ml/gcc-patches/2004-08/msg02011.html
Opencode the sincos[f] libcall.
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None of the FPStack instructions are handled in
X86RegisterInfo::foldMemoryOperand, which prevents the spiller from
folding spill code into the instructions.
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Currently the x86 codegen isn't very good at mixing SSE and FPStack
code:
unsigned int foo(double x) { return x; }
foo:
subl $20, %esp
movsd 24(%esp), %xmm0
movsd %xmm0, 8(%esp)
fldl 8(%esp)
fisttpll (%esp)
movl (%esp), %eax
addl $20, %esp
ret
This just requires being smarter when custom expanding fptoui.
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