AArch64: Fold shqri/testl/jcc into cmp/jcc

[david-arm]

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.

[meta-codesync]

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[meteorfox]

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.

[david-arm]

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.

[david-arm]

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.

[facebook-github-bot]

@david-arm has updated the pull request. You must reimport the pull request before landing.

[meteorfox]

Thanks it builds and passes tests now