B3 patchpoints should allow specifying output constraints

B3 patchpoints should allow specifying output constraints
https://bugs.webkit.org/show_bug.cgi?id=151809

Reviewed by Benjamin Poulain.

JS call patchpoints should put their result into the result register, while most other patchpoints
should put their results into some register. I think that it's best if we just allow arbitrary
constraints on the result of a patchpoint. And by "arbitrary" I mean allowing the same kinds of
constraints as we allow on the stackmap children.

This also adds a large comment in B3StackmapValue.h that lays out the philosophy of our stackmaps
and patchpoints. I found it useful to write down the plan since it's pretty subtle.

* b3/B3LowerToAir.cpp:
(JSC::B3::Air::LowerToAir::lower):
* b3/B3PatchpointSpecial.cpp:
(JSC::B3::PatchpointSpecial::isValid):
(JSC::B3::PatchpointSpecial::admitsStack):
* b3/B3PatchpointValue.cpp:
(JSC::B3::PatchpointValue::~PatchpointValue):
(JSC::B3::PatchpointValue::dumpMeta):
(JSC::B3::PatchpointValue::PatchpointValue):
* b3/B3PatchpointValue.h:
(JSC::B3::PatchpointValue::accepts):
* b3/B3Procedure.h:
(JSC::B3::Procedure::code):
* b3/B3StackmapSpecial.cpp:
(JSC::B3::StackmapSpecial::isValidImpl):
(JSC::B3::StackmapSpecial::appendRepsImpl):
(JSC::B3::StackmapSpecial::isArgValidForValue):
(JSC::B3::StackmapSpecial::isArgValidForRep):
(JSC::B3::StackmapSpecial::repForArg):
* b3/B3StackmapSpecial.h:
* b3/B3StackmapValue.h:
* b3/B3Validate.cpp:
* b3/B3ValueRep.h:
(JSC::B3::ValueRep::doubleValue):
* b3/testb3.cpp:
(JSC::B3::testPatchpointManyImms):
(JSC::B3::testPatchpointWithRegisterResult):
(JSC::B3::testPatchpointWithStackArgumentResult):
(JSC::B3::testPatchpointWithAnyResult):
(JSC::B3::testSimpleCheck):
(JSC::B3::run):
* jit/RegisterSet.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@193386 268f45cc-cd09-0410-ab3c-d52691b4dbfc