[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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@@ -0,0 +1,27 @@
+; RUN: llc -mtriple x86_64-linux-gnu -data-sections %s -o - | FileCheck %s --check-prefix=ELF
+; RUN: llc -mtriple x86_64-linux-gnu -unique-section-names=0 -data-sections %s -o - | FileCheck %s --check-prefix=ELF-NOUNIQ
+
+; RUN: llc -mtriple x86_64-windows-msvc -data-sections %s -o - | FileCheck %s --check-prefix=COFF-MSVC
+
+; ELF: .section .data.hot.foo,
+; ELF: .section .data.bar,
+; ELF: .section .bss.unlikely.baz,
+; ELF: .section .bss.quz,
+
+; ELF-NOUNIQ: .section    .data.hot.,"aw", at progbits,unique,1
+; ELF-NOUNIQ: .section    .data,"aw", at progbits,unique,2
+; ELF-NOUNIQ: .section    .bss.unlikely.,"aw", at nobits,unique,3
+; ELF-NOUNIQ: .section    .bss,"aw", at nobits,unique,4
+
+; COFF-MSVC: .section .data,"dw",one_only,foo
+; COFF-MSVC: .section .data,"dw",one_only,bar
+; COFF-MSVC: .section .bss,"bw",one_only,baz
+; COFF-MSVC: .section .bss,"bw",one_only,quz
+
+ at foo = global i32 1, !section_prefix !0
+ at bar = global i32 2
+ at baz = global i32 0, !section_prefix !1
+ at quz = global i32 0
+
+!0 = !{!"section_prefix", !"hot"}
+!1 = !{!"section_prefix", !"unlikely"}
----------------
mingmingl-llvm wrote:

Function and global variables are derived classes of GlobalObject, and currently function section prefix metadata has `function_section_prefix`.

To me, `data_section_prefix` carries the semantic that a global variable/object is a piece of data, which may become inaccurate. Alternative to setting global object's section prefix, I can keep function's methods as they are in TOT, and implements `{set,get,update}SectionPrefix` for GlobalVariables (not its superclass GlobalObject) and name it `global_variable_section_prefix`. How does that sound? 

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