Merge constant array and structures. This will create a global variables for arrays and structs that are constant and their initializer is constant. It is on by default but can be disable with the flag -fno-merge-all-constants.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@85991 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 18 insertions, 0 deletions

diff --git a/lib/CodeGen/CGDecl.cpp b/lib/CodeGen/CGDecl.cpp
index 4f8aef420d..b1ceb46277 100644
--- a/lib/CodeGen/CGDecl.cpp
+++ b/lib/CodeGen/CGDecl.cpp
@@ -19,6 +19,7 @@
 #include "clang/AST/DeclObjC.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
+#include "clang/Frontend/CompileOptions.h"
 #include "llvm/GlobalVariable.h"
 #include "llvm/Intrinsics.h"
 #include "llvm/Target/TargetData.h"
@@ -316,6 +317,20 @@ void CodeGenFunction::EmitLocalBlockVarDecl(const VarDecl &D) {
   llvm::Value *DeclPtr;
   if (Ty->isConstantSizeType()) {
     if (!Target.useGlobalsForAutomaticVariables()) {
+      
+      // All constant structs and arrays should be global if
+      // their initializer is constant and if the element type is POD.
+      if (CGM.getCompileOpts().MergeAllConstants) {
+        if (Ty.isConstant(getContext())
+            && (Ty->isArrayType() || Ty->isRecordType())
+            && (D.getInit() 
+                && D.getInit()->isConstantInitializer(getContext()))
+            && Ty->isPODType()) {
+          EmitStaticBlockVarDecl(D);
+          return;
+        }
+      }
+      
       // A normal fixed sized variable becomes an alloca in the entry block.
       const llvm::Type *LTy = ConvertTypeForMem(Ty);
       Align = getContext().getDeclAlignInBytes(&D);
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index 521c90dc31..b4c27a24e3 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -703,6 +703,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back("--debug-pass=Structure");
   if (Args.hasArg(options::OPT_fdebug_pass_arguments))
     CmdArgs.push_back("--debug-pass=Arguments");
+  if (!Args.hasFlag(options::OPT_fmerge_all_constants,
+                    options::OPT_fno_merge_all_constants))
+    CmdArgs.push_back("--no-merge-all-constants");
 
   // This is a coarse approximation of what llvm-gcc actually does, both
   // -fasynchronous-unwind-tables and -fnon-call-exceptions interact in more