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

[Snehasish Kumar via llvm-commits]

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@@ -46,6 +49,20 @@ class StaticDataSplitter : public MachineFunctionPass {
   const MachineBlockFrequencyInfo *MBFI = nullptr;
   const ProfileSummaryInfo *PSI = nullptr;
 
+  // If the global value is a local linkage global variable, return it.
+  // Otherwise, return nullptr.
+  const GlobalVariable *getLocalLinkageGlobalVariable(const GlobalValue *GV);
+
+  // Returns true if the global variable is in one of {.rodata, .bss, .data,
+  // .data.rel.ro} sections
+  bool inStaticDataSection(const GlobalVariable *GV, const TargetMachine &TM);
+
+  // Iterate all global variables in the module and update the section prefix
+  // of the module-internal data.
+  bool updateGlobalVariableSectionPrefix(MachineFunction &MF);
+
+  // Accummulated data profile count across machine functions in the module.
+  DenseMap<const GlobalVariable *, APInt> DataProfileCounts;
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snehasish wrote:

Is there a strong reason to use APInt as the value? When passed to the `isColdCount` API we extract the value as a uint64_t anyway (with an assertion). I think if you are concerned about overflows then we can use `AddOverflow` from `Support/MathExtras.h` on L163 and add an assert. Additionally, there we could use a saturating count using `getInstrMaxCountValue` as the limit if we do have cases which overflow. Wdyt?

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