clang/test/CodeGenCXX/pass-by-value-noalias.cpp

   1 // RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=WITH_NOALIAS %s
   2 // RUN: %clang_cc1 -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
   3
   4 // A trivial struct large enough so it is not passed in registers on ARM64.
   5 struct Foo {
   6   int a;
   7   int b;
   8   int c;
   9   int d;
  10   int e;
  11   int f;
  12 };
  13
  14 // Make sure noalias is added to indirect arguments with trivially copyable types
  15 // if -fpass-by-value-is-noalias is provided.
  16
  17 // WITH_NOALIAS: define{{.*}} void @_Z4take3Foo(ptr noalias noundef %arg)
  18 // NO_NOALIAS: define{{.*}} void @_Z4take3Foo(ptr noundef %arg)
  19 void take(Foo arg) {}
  20
  21 int G;
  22
  23 // NonTrivial is not trivially-copyable, because it has a non-trivial copy
  24 // constructor.
  25 struct NonTrivial {
  26   int a;
  27   int b;
  28   int c;
  29   int d;
  30   int e;
  31   int f;
  32
  33   NonTrivial(const NonTrivial &Other) {
  34     a = G + 10 + Other.a;
  35   }
  36 };
  37
  38 // Make sure noalias is not added to indirect arguments that are not trivially
  39 // copyable even if -fpass-by-value-is-noalias is provided.
  40
  41 // WITH_NOALIAS: define{{.*}} void @_Z4take10NonTrivial(ptr noundef %arg)
  42 // NO_NOALIAS:   define{{.*}} void @_Z4take10NonTrivial(ptr noundef %arg)
  43 void take(NonTrivial arg) {}
  44
  45 // Escape examples. Pointers to the objects passed to take() may escape, depending on whether a temporary copy is created or not (e.g. due to NRVO).
  46 struct A {
  47   A(A **where) : data{"hello world 1"} {
  48     *where = this; //Escaped pointer 1 (proposed UB?)
  49   }
  50
  51   A() : data{"hello world 2"} {}
  52
  53   char data[32];
  54 };
  55 A *p;
  56
  57 // WITH_NOALIAS: define{{.*}} void @_Z4take1A(ptr noalias noundef %arg)
  58 // NO_NOALIAS: define{{.*}} void @_Z4take1A(ptr noundef %arg)
  59 void take(A arg) {}
  60
  61 // WITH_NOALIAS: define{{.*}} void @_Z7CreateAPP1A(ptr noalias sret(%struct.A) align 1 %agg.result, ptr noundef %where)
  62 // NO_NOALIAS: define{{.*}} void @_Z7CreateAPP1A(ptr noalias sret(%struct.A) align 1 %agg.result, ptr noundef %where)
  63 A CreateA(A **where) {
  64   A justlikethis;
  65   *where = &justlikethis; //Escaped pointer 2 (should also be UB, then)
  66   return justlikethis;
  67 }
  68
  69 // elsewhere, perhaps compiled by a smarter compiler that doesn't make a copy here
  70 void test() {
  71   take({&p});        // 1
  72   take(CreateA(&p)); // 2
  73 }