CodeGen: Emit constant temporaries into read-only globals.

Instead of creating a copy on the stack just stash them in a private
constant global. This saves both the copying overhead and the stack
space, and gives the optimizer more room to constant fold.

This tries to make array temporaries more similar to regular arrays,
they can't use the same logic because a temporary has no VarDecl to be
bound to so we roll our own version here.

The original use case for this optimization was code like
  for (int i : {1, 2, 3, 4, 5, 6, 7, 8, 10})
    foo(i);
where without this patch (assuming that the loop is not unrolled) we
would alloca an array on the stack, copy the 10 values over and
iterate on that. With this patch we put the array in .text use it
directly. Apart from that case this helps on virtually any passing of
a constant std::initializer_list as a function argument.

Differential Revision: http://reviews.llvm.org/D8034

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@231508 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 28 insertions, 11 deletions

diff --git a/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp b/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp
index d68ba7c753..f079311e7e 100644
--- a/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp
+++ b/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp
@@ -72,6 +72,9 @@ namespace thread_local_global_array {
 // CHECK: @[[PARTLY_CONSTANT_SECOND:_ZGRN15partly_constant2ilE.*]] = internal global [2 x i32] zeroinitializer, align 4
 // CHECK: @[[PARTLY_CONSTANT_THIRD:_ZGRN15partly_constant2ilE.*]] = internal constant [4 x i32] [i32 5, i32 6, i32 7, i32 8], align 4
 
+// CHECK: @[[REFTMP1:.*]] = private constant [2 x i32] [i32 42, i32 43], comdat($_ZN7PR204451fILi0EEEvv), align 4
+// CHECK: @[[REFTMP2:.*]] = private constant [3 x %{{.*}}] [%{{.*}} { i32 1 }, %{{.*}} { i32 2 }, %{{.*}} { i32 3 }], align 4
+
 // CHECK: appending global
 
 
@@ -215,17 +218,16 @@ void fn9() {
 
 struct haslist1 {
   std::initializer_list<int> il;
-  haslist1();
+  haslist1(int i);
 };
 
-// CHECK-LABEL: define void @_ZN8haslist1C2Ev
-haslist1::haslist1()
+// CHECK-LABEL: define void @_ZN8haslist1C2Ei
+haslist1::haslist1(int i)
 // CHECK: alloca [3 x i32]
-// CHECK: store i32 1
+// CHECK: store i32 %
 // CHECK: store i32 2
 // CHECK: store i32 3
-// CHECK: store i{{32|64}} 3
-  : il{1, 2, 3}
+  : il{i, 2, 3}
 {
   destroyme2 dm2;
 }
@@ -244,16 +246,15 @@ haslist2::haslist2()
   // CHECK: call void @_ZN10destroyme1D1Ev
 }
 
-void fn10() {
-  // CHECK-LABEL: define void @_Z4fn10v
+void fn10(int i) {
+  // CHECK-LABEL: define void @_Z4fn10i
   // CHECK: alloca [3 x i32]
   // CHECK: call noalias i8* @_Znw{{[jm]}}
-  // CHECK: store i32 1
+  // CHECK: store i32 %
   // CHECK: store i32 2
   // CHECK: store i32 3
   // CHECK: store i32*
-  // CHECK: store i{{32|64}} 3
-  (void) new std::initializer_list<int> {1, 2, 3};
+  (void) new std::initializer_list<int> {i, 2, 3};
 }
 
 void fn11() {
@@ -462,6 +463,22 @@ namespace PR20445 {
   template<int x> void f() { new MyClass({42, 43}); }
   template void f<0>();
   // CHECK-LABEL: define {{.*}} @_ZN7PR204451fILi0EEEvv(
+  // CHECK: store i32* getelementptr inbounds ([2 x i32]* @[[REFTMP1]], i64 0, i64 0)
   // CHECK: call void @_ZN7PR204456vectorC1ESt16initializer_listIiE(
   // CHECK: call void @_ZN7PR204457MyClassC1ERKNS_6vectorE(
 }
+
+namespace ConstExpr {
+  class C {
+    int x;
+  public:
+    constexpr C(int x) : x(x) {}
+  };
+  void f(std::initializer_list<C>);
+  void g() {
+// CHECK-LABEL: _ZN9ConstExpr1gEv
+// CHECK: store %"class.ConstExpr::C"* getelementptr inbounds ([3 x %"class.ConstExpr::C"]* @[[REFTMP2]], i64 0, i64 0)
+// CHECK: call void @_ZN9ConstExpr1fESt16initializer_listINS_1CEE
+    f({C(1), C(2), C(3)});
+  }
+}