[LLVMdev] Semantics of an Inbounds GetElementPtr

[Nicholas White]

Thanks - that makes sense. It's interesting that at -O3 the optimizer
can't reduce the below though - I'll dig into it a bit and see if I
can make a patch that fixes it:

target datalayout = "e-i64:64-f80:128-n8:16:32:64-S128"

%struct.my_s = type { i32, i32, [0 x i8*] }

; Function Attrs: noreturn
declare void @__assert_rtn()

define void @func(i8* %mem) {
  %1 = icmp eq i8* %mem, null
  br i1 %1, label %check.zero, label %stash.zero

stash.zero:
  %2 = bitcast i8* %mem to %struct.my_s*
  %3 = getelementptr inbounds i8, i8* %mem, i64 4
  %4 = bitcast i8* %3 to i32*
  store i32 0, i32* %4, align 4
  br label %check.zero

check.zero:
  %.0.i = phi %struct.my_s* [ %2, %stash.zero ], [ null, %0 ]
  %5 = getelementptr inbounds %struct.my_s, %struct.my_s* %.0.i, i64 0, i32 1
  %6 = load i32, i32* %5, align 4
  %7 = icmp eq i32 %6, 0
  br i1 %7, label %success, label %check.first.array.element

check.first.array.element:
  %8 = getelementptr inbounds %struct.my_s, %struct.my_s* %.0.i, i64
0, i32 2, i64 0
  %9 = load i8*, i8** %8, align 1
  %10 = icmp eq i8* %9, null
  br i1 %10, label %success, label %abort

abort:
  tail call void @__assert_rtn()
  unreachable

success:
  ret void
}

Thanks -

Nick