[ndk] Add -disable-global-ctor-const-promotion option.

The global variable optimization will try to evaluate the
constant global variable and remove the constructors.

However, some legacy code will try to perform const_cast<>()
and assign to the "constant" to avoid static initialization
order fiasco.  To workaround those old code, this commit
adds a new option to disable the promotion of the global
constant with constructors.

Change-Id: If5146f1ebc9139008b5899cd474c5f57aef0697a

2 files changed, 71 insertions, 4 deletions

diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp
index 2ea89a16d86..031d0fdc105 100644
--- a/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/lib/Transforms/IPO/GlobalOpt.cpp
@@ -32,6 +32,7 @@
 #include "llvm/IR/Operator.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/CallSite.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
@@ -61,6 +62,12 @@ STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
 STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
 STATISTIC(NumCXXDtorsRemoved, "Number of global C++ destructors removed");
 
+static cl::opt<bool> DisableGlobalCtorConstPromotion(
+  "disable-global-ctor-const-promotion",
+  cl::desc("Disable constant promotion of global constants with constructors."),
+  cl::init(false),
+  cl::Hidden);
+
 namespace {
   struct GlobalOpt : public ModulePass {
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
@@ -2796,10 +2803,11 @@ static bool EvaluateStaticConstructor(Function *F, const DataLayout *TD,
            Eval.getMutatedMemory().begin(), E = Eval.getMutatedMemory().end();
          I != E; ++I)
       CommitValueTo(I->second, I->first);
-    for (SmallPtrSet<GlobalVariable*, 8>::const_iterator I =
-           Eval.getInvariants().begin(), E = Eval.getInvariants().end();
-         I != E; ++I)
-      (*I)->setConstant(true);
+    if (!DisableGlobalCtorConstPromotion)
+      for (SmallPtrSet<GlobalVariable*, 8>::const_iterator I =
+             Eval.getInvariants().begin(), E = Eval.getInvariants().end();
+           I != E; ++I)
+        (*I)->setConstant(true);
   }
 
   return EvalSuccess;
diff --git a/test/Transforms/GlobalOpt/disable-global-ctor-const-promotion.ll b/test/Transforms/GlobalOpt/disable-global-ctor-const-promotion.ll
new file mode 100644
index 00000000000..eeee3d30ebc
--- /dev/null
+++ b/test/Transforms/GlobalOpt/disable-global-ctor-const-promotion.ll
@@ -0,0 +1,59 @@
+; Test -disable-global-ctor-const-promotion
+;
+; The global variable optimization will try to evaluate the constant
+; global variable and remove the constructors.
+;
+; However, some legacy code will try to perform const_cast<>() and
+; assign to the "constant" to avoid static initialization order fiasco.
+; To workaround those old code, we would like to provide an option to
+; disable this optimization.
+;
+; This test will check whether the -disable-global-ctor-const-promotion
+; is working as expected or not.
+
+; RUN: opt < %s -globalopt -S -o - | FileCheck %s --check-prefix=CHECK-DEFAULT
+; RUN: opt < %s -globalopt -disable-global-ctor-const-promotion -S -o - \
+; RUN:   | FileCheck %s --check-prefix=CHECK-DISABLE
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%class.ConstantValue = type { i32 }
+
+@_ZL3one = internal global %class.ConstantValue zeroinitializer, align 4
+; CHECK-DEFAULT: @_ZL3one = internal constant %class.ConstantValue { i32 1 }, align 4
+; CHECK-DISABLE: @_ZL3one = internal global %class.ConstantValue { i32 1 }, align 4
+
+@llvm.global_ctors = appending global [1 x { i32, void ()* }] [{ i32, void ()* } { i32 65535, void ()* @_GLOBAL__I_a }]
+
+@_ZN13ConstantValueC1Ei = alias weak_odr void (%class.ConstantValue*, i32)* @_ZN13ConstantValueC2Ei
+
+define internal void @__cxx_global_var_init() section ".text.startup" {
+entry:
+  call void @_ZN13ConstantValueC1Ei(%class.ConstantValue* @_ZL3one, i32 1)
+  %0 = call {}* @llvm.invariant.start(i64 4, i8* bitcast (%class.ConstantValue* @_ZL3one to i8*))
+  ret void
+}
+
+declare {}* @llvm.invariant.start(i64, i8* nocapture) nounwind
+
+define void @_Z3barv() nounwind uwtable {
+entry:
+  call void @_Z3fooRK13ConstantValue(%class.ConstantValue* @_ZL3one) nounwind
+  ret void
+}
+
+declare void @_Z3fooRK13ConstantValue(%class.ConstantValue*) nounwind
+
+define linkonce_odr void @_ZN13ConstantValueC2Ei(%class.ConstantValue* %this, i32 %i) unnamed_addr nounwind uwtable align 2 {
+entry:
+  %value_ = getelementptr inbounds %class.ConstantValue* %this, i32 0, i32 0
+  store i32 %i, i32* %value_, align 4
+  ret void
+}
+
+define internal void @_GLOBAL__I_a() section ".text.startup" {
+entry:
+  call void @__cxx_global_var_init()
+  ret void
+}