[llvm-dev] [RFC] Moving llvm.dbg.value out of the instruction stream (original) (raw)

Matthias Braun via llvm-dev llvm-dev at lists.llvm.org
Tue Oct 23 10:11:40 PDT 2018

On Oct 23, 2018, at 9:53 AM, Adrian Prantl via llvm-dev <llvm-dev at lists.llvm.org> wrote:

[resending with a bugfix s/x/y/ in my example] We still have to support constant dbg.values that need to be at a specific point in the instruction stream and don't refer to any SSA value. For example, we can still have code like this: int x = foo(); int y = 42; bar(); y = x; baz(); that might lower into IR like %x = call i32 @foo() call void @llvm.dbg.value(i32 %x, DIVariable("x"), ...) call void @llvm.dbg.value(i32 42, DIVariable("y"), ...) call void @bar() call void @llvm.dbg.value(i32 %x, DIVariable("y"), ...) ; %x is not materialized here, and we also can't hoist this. call void @foo()

Maybe I am misunderstanding the proposal, but I would imagine this to be modeled similar to this:

%x = call i32 @foo() !debug-variable X0, !debug-variable Y1 call @bar() call @foo()

now we have two tables for the X and Y debug variables:

X0 (line xxx-yyy)

Y0 - Constant 42 (line xxx-yyy) Y1 (line yyy-zzz)

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