Implement the proposed design for RyuJIT's LIR. (#6689)

These changes implement the design for RyuJIT's LIR described in https://github.com/dotnet/coreclr/blob/master/Documentation/design-docs/removing-embedded-statements.md.

The following passes required changes:

Rationalize, which has been almost completely rewritten
Long decomposition
Target-independent lowering
Target-dependent lowering
LSRA
Liveness
Flowgraph optimization
Codegen
For the most part, these changes are confined to the backend. Common code that needed to be updated included liveness, flowgraph optimization, and a few miscellaneous utilities.

The utilities used to analyze and manipulate LIR live (almost) entirely in src/jit/lir.{cpp,h}. The core concepts that are unique to LIR are LIR::Use and LIR::Range. The latter is a tuple that captures an SDSU def (i.e. an LIR node) and its corresponding use->def edge and user. The former serves to abstract a self-contained sequence of LIR nodes that make up e.g. the contents of a basic block.

Testing indicates that neither JIT throughput nor code quality are significantly impacted by these changes.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/jit/codegeninterface.h b/src/jit/codegeninterface.h
index f5eec89d33..e9abbe6b3c 100644
--- a/src/jit/codegeninterface.h
+++ b/src/jit/codegeninterface.h
@@ -144,8 +144,10 @@ protected:
     void genUpdateLife(GenTreePtr tree);
     void genUpdateLife(VARSET_VALARG_TP newLife);
 
+#ifdef LEGACY_BACKEND
     regMaskTP genLiveMask(GenTreePtr tree);
     regMaskTP genLiveMask(VARSET_VALARG_TP liveSet);
+#endif
 
     void genGetRegPairFromMask(regMaskTP regPairMask, regNumber* pLoReg, regNumber* pHiReg);