[llvm] [CodeGen][StaticDataPartitioning]Place local-linkage global variables in hot or unlikely prefixed sections based on profile information (PR #125756)

[Mingming Liu via llvm-commits]

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@@ -117,18 +142,89 @@ bool StaticDataSplitter::partitionStaticDataWithProfiles(MachineFunction &MF) {
           // Hotness is based on source basic block hotness.
           // TODO: PSI APIs are about instruction hotness. Introduce API for
           // data access hotness.
-          if (PSI->isColdBlock(&MBB, MBFI))
+          if (Count && PSI->isColdCount(*Count))
             Hotness = MachineFunctionDataHotness::Cold;
 
           if (MJTI->updateJumpTableEntryHotness(JTI, Hotness))
             ++NumChangedJumpTables;
+        } else if (Op.isGlobal()) {
+          // Find global variables with local linkage
+          const GlobalVariable *GV =
+              getLocalLinkageGlobalVariable(Op.getGlobal());
+          if (!GV || !inStaticDataSection(GV, TM))
+            continue;
+
+          // Acccumulate data profile count across machine function
+          // instructions.
+          // TODO: Analyze global variable's initializers.
+          if (Count) {
+            auto [It, Inserted] =
+                DataProfileCounts.try_emplace(GV, APInt(128, 0));
+            It->second += *Count;
+          }
         }
       }
     }
   }
   return NumChangedJumpTables > 0;
 }
 
+const GlobalVariable *
+StaticDataSplitter::getLocalLinkageGlobalVariable(const GlobalValue *GV) {
+  if (!GV || GV->isDeclarationForLinker())
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mingmingl-llvm wrote:

Good question. I haven't thought about it before.

It turns out IR verifier [requires](https://github.com/llvm/llvm-project/blob/3e2afe5f019b7a1c60e23cb2743018bd2d0417b1/llvm/lib/IR/Verifier.cpp#L735-L736) a declaration to have one of 'valid' decl linkages, and valid decl linkages must be at least external according to [isValidDeclarationLinkage](https://github.com/llvm/llvm-project/blob/3e2afe5f019b7a1c60e23cb2743018bd2d0417b1/llvm/include/llvm/IR/GlobalValue.h#L420).

I removed `GV->isDeclarationForLinker()` here and added a comment.

https://github.com/llvm/llvm-project/pull/125756