[llvm] Implement pragma clang section on COFF targets

This patch implements the directive pragma clang section on
COFF targets with the exact same features available on ELF
and Mach-O.

Author: vtz

clang/docs/LanguageExtensions.rst

@@ -5531,7 +5531,7 @@ The ``#pragma clang section`` directive obeys the following rules:
 
 * The pragma clang section is enabled automatically, without need of any flags.
 
-* This feature is only defined to work sensibly for ELF and Mach-O targets.
+* This feature is only defined to work sensibly for ELF, Mach-O and COFF targets.
 
 * If section name is specified through _attribute_((section("myname"))), then
   the attribute name gains precedence.

clang/docs/ReleaseNotes.rst

@@ -845,6 +845,8 @@ Windows Support
   When `-fms-compatibility-version=18.00` or prior is set on the command line this Microsoft extension is still
   allowed as VS2013 and prior allow it.
 
+- Clang now supports the ``#pragma clang section`` directive for COFF targets.
+
 LoongArch Support
 ^^^^^^^^^^^^^^^^^
 

clang/test/Sema/pragma-clang-section.c

@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s -triple arm-none-eabi
+// RUN: %clang_cc1 -fsyntax-only -verify %s -triple arm64-windows-msvc
 #pragma clang section bss = "mybss.1" data = "mydata.1" rodata = "myrodata.1" text = "mytext.1" // expected-note 2 {{#pragma entered here}}
 #pragma clang section bss="" data="" rodata="" text=""
 #pragma clang section

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -781,29 +781,32 @@ getGlobalObjectInfo(const GlobalObject *GO, const TargetMachine &TM) {
   return {Group, IsComdat, Flags};
 }
 
-static MCSection *selectExplicitSectionGlobal(
-    const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM,
-    MCContext &Ctx, Mangler &Mang, unsigned &NextUniqueID,
-    bool Retain, bool ForceUnique) {
-  StringRef SectionName = GO->getSection();
-
+static StringRef handlePragmaClangSection(const GlobalObject *GO, SectionKind Kind) {
   // Check if '#pragma clang section' name is applicable.
   // Note that pragma directive overrides -ffunction-section, -fdata-section
   // and so section name is exactly as user specified and not uniqued.
   const GlobalVariable *GV = dyn_cast<GlobalVariable>(GO);
   if (GV && GV->hasImplicitSection()) {
     auto Attrs = GV->getAttributes();
-    if (Attrs.hasAttribute("bss-section") && Kind.isBSS()) {
-      SectionName = Attrs.getAttribute("bss-section").getValueAsString();
-    } else if (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly()) {
-      SectionName = Attrs.getAttribute("rodata-section").getValueAsString();
-    } else if (Attrs.hasAttribute("relro-section") && Kind.isReadOnlyWithRel()) {
-      SectionName = Attrs.getAttribute("relro-section").getValueAsString();
-    } else if (Attrs.hasAttribute("data-section") && Kind.isData()) {
-      SectionName = Attrs.getAttribute("data-section").getValueAsString();
-    }
+    if (Attrs.hasAttribute("bss-section") && Kind.isBSS())
+      return Attrs.getAttribute("bss-section").getValueAsString();
+    else if (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly())
+      return Attrs.getAttribute("rodata-section").getValueAsString();
+    else if (Attrs.hasAttribute("relro-section") && Kind.isReadOnlyWithRel())
+      return Attrs.getAttribute("relro-section").getValueAsString();
+    else if (Attrs.hasAttribute("data-section") && Kind.isData())
+      return Attrs.getAttribute("data-section").getValueAsString();
   }
 
+  return GO->getSection();
+}
+
+static MCSection *selectExplicitSectionGlobal(
+    const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM,
+    MCContext &Ctx, Mangler &Mang, unsigned &NextUniqueID,
+    bool Retain, bool ForceUnique) {
+  StringRef SectionName = handlePragmaClangSection(GO, Kind);
+
   // Infer section flags from the section name if we can.
   Kind = getELFKindForNamedSection(SectionName, Kind);
 
@@ -1284,21 +1287,7 @@ static void checkMachOComdat(const GlobalValue *GV) {
 MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
 
-  StringRef SectionName = GO->getSection();
-
-  const GlobalVariable *GV = dyn_cast<GlobalVariable>(GO);
-  if (GV && GV->hasImplicitSection()) {
-    auto Attrs = GV->getAttributes();
-    if (Attrs.hasAttribute("bss-section") && Kind.isBSS()) {
-      SectionName = Attrs.getAttribute("bss-section").getValueAsString();
-    } else if (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly()) {
-      SectionName = Attrs.getAttribute("rodata-section").getValueAsString();
-    } else if (Attrs.hasAttribute("relro-section") && Kind.isReadOnlyWithRel()) {
-      SectionName = Attrs.getAttribute("relro-section").getValueAsString();
-    } else if (Attrs.hasAttribute("data-section") && Kind.isData()) {
-      SectionName = Attrs.getAttribute("data-section").getValueAsString();
-    }
-  }
+  StringRef SectionName = handlePragmaClangSection(GO, Kind);
 
   // Parse the section specifier and create it if valid.
   StringRef Segment, Section;
@@ -1667,7 +1656,7 @@ static int getSelectionForCOFF(const GlobalValue *GV) {
 
 MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
-  StringRef Name = GO->getSection();
+  StringRef Name = handlePragmaClangSection(GO, Kind);
   if (Name == getInstrProfSectionName(IPSK_covmap, Triple::COFF,
                                       /*AddSegmentInfo=*/false) ||
       Name == getInstrProfSectionName(IPSK_covfun, Triple::COFF,
@@ -1677,6 +1666,7 @@ MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
       Name == getInstrProfSectionName(IPSK_covname, Triple::COFF,
                                       /*AddSegmentInfo=*/false))
     Kind = SectionKind::getMetadata();
+
   int Selection = 0;
   unsigned Characteristics = getCOFFSectionFlags(Kind, TM);
   StringRef COMDATSymName = "";

llvm/test/CodeGen/ARM/clang-section.ll

@@ -1,4 +1,5 @@
 ;RUN: llc -mtriple=armv7-eabi %s -o - | FileCheck %s
+;RUN: llc -mtriple=armv7-msvc %s -o - | FileCheck %s
 ;Test that global variables and functions are assigned to correct sections.
 
 target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"