[PATCH] D144701: [COFF] Put jump table in .rdata for Windows

[Wei Xiao via Phabricator via llvm-commits]

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Put jump table in .rdata for Windows to align with that for Linux.
It can avoid loading the same code page into I$ and D$ simultaneously
and thus favor performance.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D144701

Files:
  llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h
  llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
  llvm/test/MC/COFF/jumptable-rdata.ll


Index: llvm/test/MC/COFF/jumptable-rdata.ll
===================================================================
--- /dev/null
+++ llvm/test/MC/COFF/jumptable-rdata.ll
@@ -0,0 +1,29 @@
+; RUN: llc -mtriple x86_64-pc-win32 < %s | FileCheck %s
+
+define void @switch_jumptable(i32 %what) nounwind {
+entry:
+  switch i32 %what, label %sw.epilog [
+    i32 0, label %sw.bb
+    i32 1, label %sw.bb
+    i32 2, label %sw.bb
+    i32 3, label %sw.bb14
+    i32 4, label %sw.bb18
+    i32 6, label %sw.bb57
+  ]
+
+sw.bb:                                            ; preds = %entry, %entry, %entry
+  ret void
+
+sw.bb14:                                          ; preds = %entry
+  ret void
+
+sw.bb18:                                          ; preds = %entry
+  ret void
+
+sw.bb57:                                          ; preds = %entry
+  ret void
+
+sw.epilog:                                        ; preds = %entry
+  ret void
+}
+; CHECK: .section        .rdata
Index: llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
===================================================================
--- llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -71,6 +71,10 @@
 using namespace llvm;
 using namespace dwarf;
 
+static cl::opt<bool> JumpTableInFunctionSection(
+    "jumptable-in-function-section", cl::Hidden, cl::init(false),
+    cl::desc("Putting Jump Table in function section"));
+
 static void GetObjCImageInfo(Module &M, unsigned &Version, unsigned &Flags,
                              StringRef &Section) {
   SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags;
@@ -1777,6 +1781,17 @@
       COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE, UniqueID);
 }
 
+bool TargetLoweringObjectFileCOFF::shouldPutJumpTableInFunctionSection(
+    bool UsesLabelDifference, const Function &F) const {
+  if (!JumpTableInFunctionSection) {
+    // We can always create relative relocations, so use another section
+    // that can be marked non-executable.
+    return false;
+  }
+  return TargetLoweringObjectFile::shouldPutJumpTableInFunctionSection(
+    UsesLabelDifference, F);
+}
+
 void TargetLoweringObjectFileCOFF::emitModuleMetadata(MCStreamer &Streamer,
                                                       Module &M) const {
   emitLinkerDirectives(Streamer, M);
Index: llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h
===================================================================
--- llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h
+++ llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h
@@ -178,6 +178,9 @@
   MCSection *getSectionForJumpTable(const Function &F,
                                     const TargetMachine &TM) const override;
 
+  bool shouldPutJumpTableInFunctionSection(bool UsesLabelDifference,
+                                           const Function &F) const override;
+
   /// Emit Obj-C garbage collection and linker options.
   void emitModuleMetadata(MCStreamer &Streamer, Module &M) const override;
 


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