clang/test/CodeGen/padding-init.c

   1 // RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=pattern %s -emit-llvm -o - | FileCheck %s
   2 // RUN: %clang_cc1 -triple x86_64-unknown-unknown -ftrivial-auto-var-init=zero %s -emit-llvm -o - | FileCheck %s
   3
   4 // C guarantees that brace-init with fewer initializers than members in the
   5 // aggregate will initialize the rest of the aggregate as-if it were static
   6 // initialization. In turn static initialization guarantees that padding is
   7 // initialized to zero bits.
   8
   9 // CHECK: @__const.partial_init.s = private unnamed_addr constant { i8, [7 x i8], i64 } { i8 42, [7 x i8] zeroinitializer, i64 0 }, align 8
  10
  11 // Technically, we could initialize this padding to non-zero because all of the
  12 // struct's members have initializers.
  13
  14 // CHECK: @__const.init_all.s = private unnamed_addr constant { i8, [7 x i8], i64 } { i8 42, [7 x i8] zeroinitializer, i64 -2401053089374216531 }, align 8
  15
  16 struct S {
  17   char c;
  18   long long l;
  19 };
  20
  21 void use(struct S*);
  22
  23 // CHECK-LABEL: @empty_braces(
  24 // CHECK:       %s = alloca
  25 // CHECK-NEXT:  call void @llvm.memset{{.*}}(ptr align 8 %s, i8 0,
  26 // CHECK-NEXT:  call void @use(ptr noundef %s)
  27 void empty_braces(void) {
  28   struct S s = {};
  29   return use(&s);
  30 }
  31
  32 // CHECK-LABEL: @partial_init(
  33 // CHECK:       %s = alloca
  34 // CHECK-NEXT:  call void @llvm.memcpy{{.*}}(ptr align 8 %s, {{.*}}@__const.partial_init.s
  35 // CHECK-NEXT:  call void @use(ptr noundef %s)
  36 void partial_init(void) {
  37   struct S s = { .c = 42 };
  38   return use(&s);
  39 }
  40
  41 // CHECK-LABEL: @init_all(
  42 // CHECK:       %s = alloca
  43 // CHECK-NEXT:  call void @llvm.memcpy{{.*}}(ptr align 8 %s, {{.*}}@__const.init_all.s
  44 // CHECK-NEXT:  call void @use(ptr noundef %s)
  45 void init_all(void) {
  46   struct S s = { .c = 42, .l = 0xdeadbeefc0fedead };
  47   return use(&s);
  48 }