facebook
AArch64: Fold shqri/testl/jcc into cmp/jcc
We often see patterns like this:
shrqi 32, %v0, %v1 testl 0x80000000, %v1 jcc CC_E, ...
but really this is the same as asking if %v0 is >= 0. Rewriting this in the form
cmp 0, %v0 jcc CC_GE, ...
saves two instructions, i.e. a lsr and a mov.
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This fails to compile with
fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:117:10: error: unused variable 'bit_num' [-Werror,-Wunused-variable]
117 | auto bit_num = folly::findLastSet<uint64_t>(Val) - 1;
| ^~~~~~~
fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:99:19: error: cannot refer to type member 'Kind' in 'HPHP::jit::Vconst const' with '.'
99 | assert(op_const.Kind != Vconst::Double);
| ^
fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:113:10: note: in instantiation of function template specialization 'HPHP::jit::arm::(anonymous namespace)::get_const_int<HPHP::jit::Vr<HPHP::jit::Reg32>>' requested here
113 | if (!get_const_int(env, tstl.s0, Val) || folly::popcount(Val) != 1)
| ^
buck-out/v2/gen/fbcode/hphp/runtime/vm/__headers__/fc799a07123e9b1d/buck-headers/hphp/runtime/vm/jit/vasm-unit.h:96:8: note: member 'Kind' declared here
96 | enum Kind { Quad, Long, Byte, Double };
| ^
fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:99:19: error: cannot refer to type member 'Kind' in 'HPHP::jit::Vconst const' with '.'
99 | assert(op_const.Kind != Vconst::Double);
| ^
fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:131:8: note: in instantiation of function template specialization 'HPHP::jit::arm::(anonymous namespace)::get_const_int<HPHP::jit::Vr<HPHP::jit::Reg64>>' requested here
131 | if (!get_const_int(env, inst.s0, Val) || Val != 0x8000000000000000ull)
| ^
buck-out/v2/gen/fbcode/hphp/runtime/vm/__headers__/fc799a07123e9b1d/buck-headers/hphp/runtime/vm/jit/vasm-unit.h:96:8: note: member 'Kind' declared here
96 | enum Kind { Quad, Long, Byte, Double };
| ^
3 errors generated.
This fails to compile with
fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:117:10: error: unused variable 'bit_num' [-Werror,-Wunused-variable] 117 | auto bit_num = folly::findLastSet<uint64_t>(Val) - 1; | ^~~~~~~ fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:99:19: error: cannot refer to type member 'Kind' in 'HPHP::jit::Vconst const' with '.' 99 | assert(op_const.Kind != Vconst::Double); | ^ fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:113:10: note: in instantiation of function template specialization 'HPHP::jit::arm::(anonymous namespace)::get_const_int<HPHP::jit::Vr<HPHP::jit::Reg32>>' requested here 113 | if (!get_const_int(env, tstl.s0, Val) || folly::popcount(Val) != 1) | ^ buck-out/v2/gen/fbcode/hphp/runtime/vm/__headers__/fc799a07123e9b1d/buck-headers/hphp/runtime/vm/jit/vasm-unit.h:96:8: note: member 'Kind' declared here 96 | enum Kind { Quad, Long, Byte, Double }; | ^ fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:99:19: error: cannot refer to type member 'Kind' in 'HPHP::jit::Vconst const' with '.' 99 | assert(op_const.Kind != Vconst::Double); | ^ fbcode/hphp/runtime/vm/jit/vasm-simplify-arm.cpp:131:8: note: in instantiation of function template specialization 'HPHP::jit::arm::(anonymous namespace)::get_const_int<HPHP::jit::Vr<HPHP::jit::Reg64>>' requested here 131 | if (!get_const_int(env, inst.s0, Val) || Val != 0x8000000000000000ull) | ^ buck-out/v2/gen/fbcode/hphp/runtime/vm/__headers__/fc799a07123e9b1d/buck-headers/hphp/runtime/vm/jit/vasm-unit.h:96:8: note: member 'Kind' declared here 96 | enum Kind { Quad, Long, Byte, Double }; | ^ 3 errors generated.
OK thanks I'll take a look! It seemed to pass for me downstream, so presumably I'm using a different build setup.
Yeah the assert(op_const.Kind != Vconst::Double); is really daft and it's weird my build didn't complain about it. Also, looks like we should be building with -Werror too.
