similar to: Tracking parts of expanded values in optimized debug

On Wed, Jul 8, 2020 at 9:29 AM Adrian Prantl via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > > > > On Jul 8, 2020, at 5:21 AM, Tozer, Stephen <stephen.tozer at sony.com> wrote: > > > >> To summarize my understanding: Neither of these operators is strictly necessary, since the same effect can be achieved by implicitly pushing all operands of a

> To summarize my understanding: Neither of these operators is strictly necessary, since the same effect can be achieved by implicitly pushing all operands of a DBG_VALUE to the stack, followed by a combination of DW_OP_dup, DW_OP_pick, DW_OP_swap, DW_OP_rot, and DW_OP_over. However, the resulting expressions can get very long and unwieldy and it is easier to generate efficient DWARF from

Currently, two patches undergoing review wish to add a new operator for LLVM's DIExpression: D70642[0], and D82363[1]. Though both of these cases use the same name, the operators have different meanings: in the former, it has the form `DW_OP_LLVM_argN` where N is in [0-7], and represents the Nth argument of the containing intrinsic; its purpose is to enable the intrinsic @llvm.dbg.derefval,

On Wed, Jul 8, 2020 at 9:48 AM Adrian Prantl <aprantl at apple.com> wrote: > > > > > On Jul 8, 2020, at 9:33 AM, David Blaikie <dblaikie at gmail.com> wrote: > > > > On Wed, Jul 8, 2020 at 9:29 AM Adrian Prantl via llvm-dev > > <llvm-dev at lists.llvm.org> wrote: > >> > >> > >> > >>> On Jul 8, 2020, at 5:21

Hi Xiang, On Wed, Nov 11, 2020 at 1:59 AM Zhang, Xiang1 <xiang1.zhang at intel.com> wrote: > Jeremy wrote: > > ... The value %0 is live up to and including the ADD64ri but not past it, meaning LLVM today will drop the DBG_VALUE ... > > Just a little puzzle about the " drop the DBG_VALUE ", maybe I didn't get your key point, >

Currently there is a series of patches undergoing review[0] that seek to enable the use of multiple IR/MIR values when describing a source variable's location. The current plan for the MIR is to add a new instruction, DBG_VALUE_LIST, that supports this functionality by having a variable number of operands. It may be better however to simply replace the existing DBG_VALUE behaviour entirely

On Wed, Sep 6, 2017 at 10:01 AM, David Blaikie <dblaikie at gmail.com> wrote: > On Tue, Sep 5, 2017 at 1:00 PM Reid Kleckner via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > >> LLVM SSA values obviously do not have an address that we can take and >> they don’t live in registers, so neither the default memory location model >> nor DW_OP_regN make sense

I chatted with Chandler in person and came up with what I think is a much simpler design than my previous design in the thread titled "RFC: Introduce DW_OP_LLVM_memory to describe variables in memory with dbg.value". The crux of the problem in that thread is that we need a representation, particularly in the middle-end, to describe a variables address, at a particular program point.

> On Sep 19, 2017, at 8:44 AM, Reid Kleckner <rnk at google.com> wrote: > > On Tue, Sep 19, 2017 at 8:40 AM, Adrian Prantl via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote: > > Later loop unroll comes and unrolls the loop and then suddenly we have two absolutely identical dbg.declares and the assert in addFragmentOffset() blows.

> On Mar 30, 2020, at 11:57 PM, Sourabh Singh Tomar <sourav0311 at gmail.com> wrote: > >> > My understanding is that this isn't correct: dbg.declare specifies the >> memory address of a variable for the whole lifetime of the function, >> whereas dbg.value (and dbg.addr) specify the value/address until the >> next debug intrinsic. Mixing these two kinds

> That makes sense, and I think for "direct" values in your definition it is true that all direct values are r-values. > Why do we need DW_OP_LLVM_direct when we already have DW_OP_LLVM_stack_value? Can you give an example of something that is definitely not a stack value, but direct? The difference in definition is the intention: DW_OP_LLVM_direct means "we'd like this

> I can see how that could potentially be useful. I'm not sure how often we could practically make use of a situation like this, but I understand your motivation. Indeed, I don't expect us to cancel out DWARF expressions like that very often. Although that edge case is likely to be very rare, the _direct operator itself will appear very frequently, as it would be used for every

On Wed, Sep 6, 2017 at 5:01 PM, David Blaikie <dblaikie at gmail.com> wrote: > On Wed, Sep 6, 2017 at 2:01 PM Reid Kleckner <rnk at google.com> wrote: > >> On Wed, Sep 6, 2017 at 10:01 AM, David Blaikie <dblaikie at gmail.com> >> wrote: >> >>> I guess you described this already, but talking it through for >>> myself/maybe others will

> I don't see how this is a meaningful distinction in LLVM IR. In LLVM IR we only have SSA values. An SSA value could be an alloca, or a gep into an alloca, or spilled onto the stack at the MIR level, in which case the dbg.value should get lowered into a memory location (if it isn't explicitly a DW_OP_stack_value). I think the distinction is still important; even at the IR level, if we

> On Apr 1, 2020, at 2:56 AM, Sourabh Singh Tomar <sourav0311 at gmail.com> wrote: > > > Do you mean documenting the desired frontend behavior, or adding some verifier in > LLVM? A warning for the latter is that SROA may currently emit IR that contains a > mix of declares and values for different fragments of an aggregate variable, so I > assume that is something that

> I'm not sure this will work as stated here. Indirectness is (mostly) orthogonal to DW_OP_stack_value. DW_OP_stack_value denotes that we reconstructed the value of the variable, but it doesn't exist in the program ("The DW_OP_stack_value operation specifies that the object does not exist in memory but its value is nonetheless known"), for example, a constant value. I think we

> Yeah, because that decision can only be made much later in LLVM in AsmPrinter/DwarfExpression.cpp. > In DWARF, DW_OP_reg(x) is a register l-value, all others can either be l-values or r-values depending on whether there is a DW_OP_stack_value/DW_OP_implicit* at the end. Yes, it might not be clear but that's what I'm trying to say. Out of the non-empty DWARF locations, register and

Hi all, Thanks for the answers! I feel like I've hijacked your thread now though Björn, sorry for that. But from the answers it sounds like there is agreement that it's reasonable to remove the duplicates as done in Björn's patch? --- A couple of more things around the problem I saw. On 09/19/2017 05:40 PM, Adrian Prantl wrote: > A dbg.declare describes a stack-allocated

Realized I didn't document the original reviews that motivated this thread: A stack of reviews, split off from here: https://reviews.llvm.org/D69787 Alok's posted a new patch (with smaller patches split off from the monolithic one) here: https://reviews.llvm.org/D84112 I haven't had a chance to page in all the old context, nor look at the new ones in detail yet. But probably worth

Debug info today handles two cases reasonably well: 1. At -O0, dbg.declare does a good job describing variables that live at some known stack offset 2. With optimizations, variables promoted to SSA can be described with dbg.value This leaves behind a large hole in our optimized debug info: variables that cannot be promoted, typically because they are address-taken. This is