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

diff --git a/lib/CodeGen/CGExpr.cpp b/lib/CodeGen/CGExpr.cpp
index 78e80a15836615314bc7c00a38386fcc8b4cfcd4..a1cbef26457ac89f47c10a7a506e42378255f504 100644 (file)
--- a/lib/CodeGen/CGExpr.cpp
+++ b/lib/CodeGen/CGExpr.cpp
@@ -301,6 +301,25 @@ createReferenceTemporary(CodeGenFunction &CGF,
   switch (M->getStorageDuration()) {
   case SD_FullExpression:
   case SD_Automatic:
+    // If we have a constant temporary array or record try to promote it into a
+    // constant global under the same rules a normal constant would've been
+    // promoted. This is easier on the optimizer and generally emits fewer
+    // instructions.
+    if (CGF.CGM.getCodeGenOpts().MergeAllConstants &&
+        (M->getType()->isArrayType() || M->getType()->isRecordType()) &&
+        CGF.CGM.isTypeConstant(M->getType(), true))
+      if (llvm::Constant *Init =
+              CGF.CGM.EmitConstantExpr(Inner, M->getType(), &CGF)) {
+        auto *GV = new llvm::GlobalVariable(
+            CGF.CGM.getModule(), Init->getType(), /*isConstant=*/true,
+            llvm::GlobalValue::PrivateLinkage, Init, ".ref.tmp");
+        GV->setAlignment(
+            CGF.getContext().getTypeAlignInChars(M->getType()).getQuantity());
+        // Put the new global in the same COMDAT the function containing the
+        // temporary is in.
+        GV->setComdat(CGF.CurFn->getComdat());
+        return GV;
+      }
     return CGF.CreateMemTemp(Inner->getType(), "ref.tmp");
 
   case SD_Thread:
@@ -370,8 +389,9 @@ EmitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *M) {
   // Create and initialize the reference temporary.
   llvm::Value *Object = createReferenceTemporary(*this, M, E);
   if (auto *Var = dyn_cast<llvm::GlobalVariable>(Object)) {
-    // If the temporary is a global and has a constant initializer, we may
-    // have already initialized it.
+    // If the temporary is a global and has a constant initializer or is a
+    // constant temporary that we promoted to a global, we may have already
+    // initialized it.
     if (!Var->hasInitializer()) {
       Var->setInitializer(CGM.EmitNullConstant(E->getType()));
       EmitAnyExprToMem(E, Object, Qualifiers(), /*IsInit*/true);

diff --git a/test/CodeGenCXX/compound-literals.cpp b/test/CodeGenCXX/compound-literals.cpp
index 2b77d2490aac70e5246a6f5ca526d304311a81da..2bbeefbe934b536ac15ff147cf6d4032b2e07e74 100644 (file)
--- a/test/CodeGenCXX/compound-literals.cpp
+++ b/test/CodeGenCXX/compound-literals.cpp
@@ -28,7 +28,7 @@ int f() {
 
 // CHECK-LABEL: define i32 @_Z1gv()
 int g() {
-  // CHECK: store [2 x i32]* %{{[a-z0-9.]+}}, [2 x i32]** [[V:%[a-z0-9.]+]]
+  // CHECK: store [2 x i32]* @{{.*}}, [2 x i32]** [[V:%[a-z0-9.]+]]
   const int (&v)[2] = (int [2]) {1,2};
 
   // CHECK: [[A:%[a-z0-9.]+]] = load [2 x i32]*, [2 x i32]** [[V]]

diff --git a/test/CodeGenCXX/cxx0x-initializer-array.cpp b/test/CodeGenCXX/cxx0x-initializer-array.cpp
index 49bc86fadc781ce934abf186d7df3d6d693f724c..de10aee67f13edbcdc62cf9eb01b95313b4baaca 100644 (file)
--- a/test/CodeGenCXX/cxx0x-initializer-array.cpp
+++ b/test/CodeGenCXX/cxx0x-initializer-array.cpp
@@ -42,10 +42,11 @@ namespace ValueInitArrayOfMemPtr {
     // CHECK: call void @llvm.memcpy.p0i8.p0i8.i32(i8* %{{.*}}, i8* bitcast ([3 x i32]* @[[THREE_NULL_MEMPTRS]] to i8*), i32 12, i32 4, i1 false)
   }
 
-  // CHECK-LABEL: define void @_ZN22ValueInitArrayOfMemPtr1gEv
-  void g() {
+  // Test dynamic initialization.
+  // CHECK-LABEL: define void @_ZN22ValueInitArrayOfMemPtr1gEMNS_1SEi
+  void g(p ptr) {
     // CHECK: store i32 -1,
-    f(a{});
+    f(a{ptr});
   }
 }
 

diff --git a/test/CodeGenCXX/cxx0x-initializer-references.cpp b/test/CodeGenCXX/cxx0x-initializer-references.cpp
index 23d244bc5674269532349179e88bf9a44cf1cb13..d4a8f20f35730f6717d5bf0461312227735b439e 100644 (file)
--- a/test/CodeGenCXX/cxx0x-initializer-references.cpp
+++ b/test/CodeGenCXX/cxx0x-initializer-references.cpp
@@ -35,22 +35,30 @@ namespace reference {
     // CHECK-NEXT: ret
   }
 
-  void reference_to_aggregate() {
+  void reference_to_aggregate(int i) {
     // CHECK: getelementptr {{.*}}, i32 0, i32 0
     // CHECK-NEXT: store i32 1
     // CHECK-NEXT: getelementptr {{.*}}, i32 0, i32 1
-    // CHECK-NEXT: store i32 2
+    // CHECK-NEXT: %[[I1:.*]] = load i32, i32*
+    // CHECK-NEXT: store i32 %[[I1]]
     // CHECK-NEXT: store %{{.*}}* %{{.*}}, %{{.*}}** %{{.*}}, align
-    const A &ra1{1, 2};
+    const A &ra1{1, i};
 
     // CHECK-NEXT: getelementptr inbounds [3 x i32], [3 x i32]* %{{.*}}, i{{32|64}} 0, i{{32|64}} 0
     // CHECK-NEXT: store i32 1
     // CHECK-NEXT: getelementptr inbounds i32, i32* %{{.*}}, i{{32|64}} 1
     // CHECK-NEXT: store i32 2
     // CHECK-NEXT: getelementptr inbounds i32, i32* %{{.*}}, i{{32|64}} 1
-    // CHECK-NEXT: store i32 3
+    // CHECK-NEXT: %[[I2:.*]] = load i32, i32*
+    // CHECK-NEXT: store i32 %[[I2]]
     // CHECK-NEXT: store [3 x i32]* %{{.*}}, [3 x i32]** %{{.*}}, align
-    const int (&arrayRef)[] = {1, 2, 3};
+    const int (&arrayRef)[] = {1, 2, i};
+
+    // CHECK: store %{{.*}}* @{{.*}}, %{{.*}}** %{{.*}}, align
+    const A &constra1{1, 2};
+
+    // CHECK-NEXT: store [3 x i32]* @{{.*}}, [3 x i32]** %{{.*}}, align
+    const int (&constarrayRef)[] = {1, 2, 3};
 
     // CHECK-NEXT: ret
   }

diff --git a/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp b/test/CodeGenCXX/cxx0x-initializer-stdinitializerlist.cpp
index d68ba7c75371007b2d495e580247688bc4af6f73..f079311e7e8ce369546067b4530785362774aafc 100644 (file)
--- 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)});
+  }
+}