JIT: Extract StructSegments to its own file (#104432)

Also move the function to compute the significant segments for a class
handle from `Promotion` to `Compiler`.

src/coreclr/jit/CMakeLists.txt

@@ -178,6 +178,7 @@ set( JIT_SOURCES
   ssabuilder.cpp
   ssarenamestate.cpp
   stacklevelsetter.cpp
+  structsegments.cpp
   switchrecognition.cpp
   treelifeupdater.cpp
   unwind.cpp
@@ -379,6 +380,7 @@ set( JIT_HEADERS
   ssaconfig.h
   ssarenamestate.h
   stacklevelsetter.h
+  structsegments.h
   target.h
   targetx86.h
   targetamd64.h

src/coreclr/jit/compiler.cpp

@@ -1990,6 +1990,7 @@ void Compiler::compInit(ArenaAllocator*       pAlloc,
     m_outlinedCompositeSsaNums = nullptr;
     m_nodeToLoopMemoryBlockMap = nullptr;
     m_signatureToLookupInfoMap = nullptr;
+    m_significantSegmentsMap   = nullptr;
     fgSsaPassesCompleted       = 0;
     fgSsaValid                 = false;
     fgVNPassesCompleted        = 0;
@@ -8373,6 +8374,67 @@ void Compiler::TransferTestDataToNode(GenTree* from, GenTree* to)
 
 #endif // DEBUG
 
+//------------------------------------------------------------------------
+// GetSignificantSegments:
+//   Compute a segment tree containing all significant (non-padding) segments
+//   for the specified class layout.
+//
+// Parameters:
+//   layout - The layout
+//
+// Returns:
+//   Segment tree containing all significant parts of the layout.
+//
+const StructSegments& Compiler::GetSignificantSegments(ClassLayout* layout)
+{
+    StructSegments* cached;
+    if ((m_significantSegmentsMap != nullptr) && m_significantSegmentsMap->Lookup(layout, &cached))
+    {
+        return *cached;
+    }
+
+    COMP_HANDLE compHnd = info.compCompHnd;
+
+    StructSegments* newSegments = new (this, CMK_Promotion) StructSegments(getAllocator(CMK_Promotion));
+
+    if (layout->IsBlockLayout())
+    {
+        newSegments->Add(StructSegments::Segment(0, layout->GetSize()));
+    }
+    else
+    {
+        CORINFO_TYPE_LAYOUT_NODE nodes[256];
+        size_t                   numNodes = ArrLen(nodes);
+        GetTypeLayoutResult      result   = compHnd->getTypeLayout(layout->GetClassHandle(), nodes, &numNodes);
+
+        if (result != GetTypeLayoutResult::Success)
+        {
+            newSegments->Add(StructSegments::Segment(0, layout->GetSize()));
+        }
+        else
+        {
+            for (size_t i = 0; i < numNodes; i++)
+            {
+                const CORINFO_TYPE_LAYOUT_NODE& node = nodes[i];
+                if ((node.type != CORINFO_TYPE_VALUECLASS) || (node.simdTypeHnd != NO_CLASS_HANDLE) ||
+                    node.hasSignificantPadding)
+                {
+                    newSegments->Add(StructSegments::Segment(node.offset, node.offset + node.size));
+                }
+            }
+        }
+    }
+
+    if (m_significantSegmentsMap == nullptr)
+    {
+        m_significantSegmentsMap = new (this, CMK_Promotion) ClassLayoutStructSegmentsMap(getAllocator(CMK_Promotion));
+    }
+
+    m_significantSegmentsMap->Set(layout, newSegments);
+
+    return *newSegments;
+}
+
 /*
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 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

src/coreclr/jit/compiler.h

@@ -43,6 +43,7 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 #include "valuenum.h"
 #include "scev.h"
 #include "namedintrinsiclist.h"
+#include "structsegments.h"
 #ifdef LATE_DISASM
 #include "disasm.h"
 #endif
@@ -5630,6 +5631,11 @@ class Compiler
         return m_signatureToLookupInfoMap;
     }
 
+    const StructSegments& GetSignificantSegments(ClassLayout* layout);
+
+    typedef JitHashTable<ClassLayout*, JitPtrKeyFuncs<ClassLayout>, class StructSegments*> ClassLayoutStructSegmentsMap;
+    ClassLayoutStructSegmentsMap* m_significantSegmentsMap;
+
 #ifdef SWIFT_SUPPORT
     typedef JitHashTable<CORINFO_CLASS_HANDLE, JitPtrKeyFuncs<struct CORINFO_CLASS_STRUCT_>, CORINFO_SWIFT_LOWERING*> SwiftLoweringMap;
     SwiftLoweringMap* m_swiftLoweringCache;