[CodeGen] Recognize more cases of zero initialization

If a variable has an initializer, codegen tries to build its value. If
the variable is large in size, building its value requires substantial
resources. It causes strange behavior from user viewpoint: compilation
of huge zero initialized arrays like:

    char data_1[2147483648u] = { 0 };

consumes enormous amount of time and memory.

With this change codegen tries to determine if variable initializer is
equivalent to zero initializer. In this case variable value is not
constructed.

This change fixes PR18978.

Differential Revision: https://reviews.llvm.org/D46241

llvm-svn: 332847

3 files changed, 3 insertions, 3 deletions

diff --git a/clang/test/CodeGen/const-init.c b/clang/test/CodeGen/const-init.c
index 3fd231b630e..2d699954031 100644
--- a/clang/test/CodeGen/const-init.c
+++ b/clang/test/CodeGen/const-init.c
@@ -167,7 +167,7 @@ void g30() {
     int : 1;
     int x;
   } a = {};
-  // CHECK: @g30.a = internal global %struct.anon.1 <{ i8 undef, i32 0 }>, align 1
+  // CHECK: @g30.a = internal global %struct.anon.1 zeroinitializer, align 1
 #pragma pack()
 }
 
diff --git a/clang/test/CodeGen/designated-initializers.c b/clang/test/CodeGen/designated-initializers.c
index 74532c8fa5b..21077b4c147 100644
--- a/clang/test/CodeGen/designated-initializers.c
+++ b/clang/test/CodeGen/designated-initializers.c
@@ -8,7 +8,7 @@ struct foo {
 // CHECK: @u = global %union.anon zeroinitializer
 union { int i; float f; } u = { };
 
-// CHECK: @u2 = global { i32, [4 x i8] } { i32 0, [4 x i8] undef }
+// CHECK: @u2 = global %union.anon.0 zeroinitializer
 union { int i; double f; } u2 = { };
 
 // CHECK: @u3 = global  %union.anon.1 zeroinitializer
diff --git a/clang/test/CodeGen/union-init2.c b/clang/test/CodeGen/union-init2.c
index bf20696a22c..0b68c211122 100644
--- a/clang/test/CodeGen/union-init2.c
+++ b/clang/test/CodeGen/union-init2.c
@@ -5,7 +5,7 @@
 union x {long long b;union x* a;} r = {.a = &r};
 
 
-// CHECK: global { [3 x i8], [5 x i8] } { [3 x i8] zeroinitializer, [5 x i8] undef }
+// CHECK: global %union.z zeroinitializer
 union z {
   char a[3];
   long long b;