Pass CompAllocator by value (#15025)

Passing CompAllocator objects by value is advantageous because it no longer needs to be dynamically allocated and cached. CompAllocator instances can now be freely created, copied and stored, which makes adding new CompMemKind values easier.

Together with other cleanup this also improves memory allocation performance by removing some extra levels of indirection that were previously required - jitstd::allocator had a pointer to CompAllocator, CompAllocator had a pointer to Compiler and Compiler finally had a pointer to ArenaAllocator. Without MEASURE_MEM_ALLOC enabled, both jitstd::allocator and CompAllocator now just contain a pointer to ArenaAllocator. When MEASURE_MEM_ALLOC is enabled CompAllocator also contains a pointer but to a MemStatsAllocator object that holds the relevant memory kind. This way CompAllocator is always pointer sized so that enabling MEASURE_MEM_ALLOC does not result in increased memory usage due to objects that store a CompAllocator instance.

In order to implement this, 2 additional signficant changes have been made:
* MemStats has been moved to ArenaAllocator, it's after all the allocator's job to maintain statistics. This also fixes some issues related to memory statistics, such as not tracking the memory allocated by the inlinee compiler (since that one used its own MemStats instance).
* Extract the arena page pooling logic out of the allocator. It doesn't make sense to pool an allocator, it has very little state that can actually be reused and everyting else (including MemStats) needs to be reset on reuse. What really needs to be pooled is just a page of memory.

Since this was touching allocation code the opportunity has been used to perform additional cleanup:
* Remove unnecessary LSRA ListElementAllocator
* Remove compGetMem and compGetMemArray
* Make CompAllocator and HostAllocator more like the std allocator
* Update HashTable to use CompAllocator
* Update ArrayStack to use CompAllocator
* Move CompAllocator & friends to alloc.h

1 files changed, 0 insertions, 102 deletions

diff --git a/src/jit/jit.h b/src/jit/jit.h
index 0e3ec9295f..f6a575d262 100644
--- a/src/jit/jit.h
+++ b/src/jit/jit.h
@@ -830,110 +830,8 @@ const int MIN_SHORT_AS_INT = -32768;
 
 /*****************************************************************************/
 
-// CompMemKind values are used to tag memory allocations performed via
-// the compiler's allocator so that the memory usage of various compiler
-// components can be tracked separately (when MEASURE_MEM_ALLOC is defined).
-
-enum CompMemKind
-{
-#define CompMemKindMacro(kind) CMK_##kind,
-#include "compmemkind.h"
-    CMK_Count
-};
-
 class Compiler;
 
-// Allows general purpose code (e.g. collection classes) to allocate memory
-// of a pre-determined kind via the compiler's allocator.
-
-class CompAllocator
-{
-    Compiler* const m_comp;
-#if MEASURE_MEM_ALLOC
-    CompMemKind const m_cmk;
-#endif
-public:
-    CompAllocator(Compiler* comp, CompMemKind cmk)
-        : m_comp(comp)
-#if MEASURE_MEM_ALLOC
-        , m_cmk(cmk)
-#endif
-    {
-    }
-
-    // Allocates a block of memory at least `sz` in size.
-    // Zero-length allocation are not allowed.
-    inline void* Alloc(size_t sz);
-
-    // Allocates a block of memory at least `elems * elemSize` in size.
-    // Zero-length allocation are not allowed.
-    inline void* ArrayAlloc(size_t elems, size_t elemSize);
-
-    // For the compiler's ArenaAllocator, free operations are no-ops.
-    void Free(void* p)
-    {
-    }
-};
-
-// Global operator new overloads that work with CompAllocator
-
-inline void* __cdecl operator new(size_t n, CompAllocator* alloc)
-{
-    return alloc->Alloc(n);
-}
-
-inline void* __cdecl operator new[](size_t n, CompAllocator* alloc)
-{
-    return alloc->Alloc(n);
-}
-
-// A CompAllocator wrapper that implements IAllocator and allows zero-length
-// memory allocations (the compiler's ArenAllocator does not support zero-length
-// allocation).
-
-class CompIAllocator : public IAllocator
-{
-    CompAllocator* const m_alloc;
-    char                 m_zeroLenAllocTarg;
-
-public:
-    CompIAllocator(CompAllocator* alloc) : m_alloc(alloc)
-    {
-    }
-
-    // Allocates a block of memory at least `sz` in size.
-    virtual void* Alloc(size_t sz) override
-    {
-        if (sz == 0)
-        {
-            return &m_zeroLenAllocTarg;
-        }
-        else
-        {
-            return m_alloc->Alloc(sz);
-        }
-    }
-
-    // Allocates a block of memory at least `elems * elemSize` in size.
-    virtual void* ArrayAlloc(size_t elemSize, size_t numElems) override
-    {
-        if ((elemSize == 0) || (numElems == 0))
-        {
-            return &m_zeroLenAllocTarg;
-        }
-        else
-        {
-            return m_alloc->ArrayAlloc(elemSize, numElems);
-        }
-    }
-
-    // Frees the block of memory pointed to by p.
-    virtual void Free(void* p) override
-    {
-        m_alloc->Free(p);
-    }
-};
-
 class JitTls
 {
 #ifdef DEBUG