Opague Pointers

[ahueck]

With future LLVM versions "opaque pointers" replace the currently typed pointers in LLVM, also eliminating the need for bitcasts.
As TypeART relies on these for determining the type of a heap allocation, adaptions are required to handle opaque pointers, e.g., relying on the DINodes.

Example: Affected test

malloc_free_double

define dso_local void @test() #0 {
  %1 = alloca double*, align 8
  %2 = bitcast double** %1 to i8*
  call void @llvm.lifetime.start.p0i8(i64 8, i8* %2) #3
  %3 = call noalias i8* @malloc(i64 noundef 336) #3
  %4 = bitcast i8* %3 to double*
  store double* %4, double** %1, align 8, !tbaa !3
  %5 = load double*, double** %1, align 8, !tbaa !3
  %6 = bitcast double* %5 to i8*
  call void @free(i8* noundef %6) #3
  %7 = bitcast double** %1 to i8*
  call void @llvm.lifetime.end.p0i8(i64 8, i8* %7) #3
  ret void
}

vs.

define dso_local void @test() #0 {
entry:
  %p = alloca ptr, align 8
  call void @llvm.lifetime.start.p0(i64 8, ptr %p) #4
  %call = call noalias ptr @malloc(i64 noundef 336) #5
  store ptr %call, ptr %p, align 8, !tbaa !5
  %0 = load ptr, ptr %p, align 8, !tbaa !5
  call void @free(ptr noundef %0) #4
  call void @llvm.lifetime.end.p0(i64 8, ptr %p) #4
  ret void
}

Affected LLVM version

Opague pointers may be default with LLVM 15.

Sources

• https://llvm.org/docs/OpaquePointers.html
• https://www.youtube.com/watch?v=qWHLf31NnNk