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8344387: RISC-V: C2: Improve encoding of LoadNKlass for compact headers #22203

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8344387: RISC-V: C2: Improve encoding of LoadNKlass for compact headers #22203

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10 changes: 0 additions & 10 deletions src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3124,13 +3124,3 @@ void C2_MacroAssembler::extract_fp_v(FloatRegister dst, VectorRegister src, Basi
vfmv_f_s(dst, tmp);
}
}

void C2_MacroAssembler::load_narrow_klass_compact_c2(Register dst, Address src) {
// The incoming address is pointing into obj-start + klass_offset_in_bytes. We need to extract
// obj-start, so that we can load from the object's mark-word instead. Usually the address
// comes as obj-start in obj and klass_offset_in_bytes in disp.
assert(UseCompactObjectHeaders, "must");
int offset = oopDesc::mark_offset_in_bytes() - oopDesc::klass_offset_in_bytes();
ld(dst, Address(src.base(), src.offset() + offset));
srli(dst, dst, markWord::klass_shift);
}
2 changes: 0 additions & 2 deletions src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.hpp
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Expand Up @@ -281,6 +281,4 @@
void extract_v(Register dst, VectorRegister src, BasicType bt, int idx, VectorRegister tmp);
void extract_fp_v(FloatRegister dst, VectorRegister src, BasicType bt, int idx, VectorRegister tmp);

void load_narrow_klass_compact_c2(Register dst, Address src);

#endif // CPU_RISCV_C2_MACROASSEMBLER_RISCV_HPP
8 changes: 6 additions & 2 deletions src/hotspot/cpu/riscv/riscv.ad
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Expand Up @@ -4814,10 +4814,14 @@ instruct loadNKlassCompactHeaders(iRegNNoSp dst, memory mem)
match(Set dst (LoadNKlass mem));

ins_cost(LOAD_COST);
format %{ "load_narrow_klass_compact $dst, $mem\t# compressed class ptr, #@loadNKlassCompactHeaders" %}
format %{
"lwu $dst, $mem\t# compressed klass ptr, shifted\n\t"
"srli $dst, $dst, markWord::klass_shift_at_offset"
%}

ins_encode %{
__ load_narrow_klass_compact_c2(as_Register($dst$$reg), Address(as_Register($mem$$base), $mem$$disp));
__ lwu(as_Register($dst$$reg), Address(as_Register($mem$$base), $mem$$disp));
__ srli(as_Register($dst$$reg), as_Register($dst$$reg), (unsigned) markWord::klass_shift_at_offset);
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@RealFYang RealFYang Nov 18, 2024 •
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Do we need this explicit unsigned type conversion?
(PS: I didn't see any issue when building without this type conversion)

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@Hamlin-Li Hamlin-Li Nov 19, 2024

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Yes, you're right here, the int will be converted to unsigned int implicitly.
I added the explicit conversion because it makes the code more clear, and in riscv.ad similar conversions are explicit (e.g. LShiftI and so on)

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@RealFYang RealFYang Nov 19, 2024

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All right then ;-)

%}

ins_pipe(iload_reg_mem);
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