On Mar 1, 2013, at 10:15 AM, Adrian Prantl <[email protected]> wrote:
> On Feb 28, 2013, at 11:20 AM, John McCall <[email protected]> wrote:
>> On Feb 28, 2013, at 11:12 AM, Eric Christopher <[email protected]> wrote:
>>> On Thu, Feb 28, 2013 at 11:06 AM, John McCall <[email protected]> wrote:
>>> On Feb 27, 2013, at 3:17 PM, Eric Christopher <[email protected]> wrote:
>>>> On Wed, Feb 27, 2013 at 11:49 AM, John McCall <[email protected]> wrote:
>>>> On Feb 27, 2013, at 11:42 AM, Eric Christopher <[email protected]> wrote:
>>>>> On Wed, Feb 27, 2013 at 11:39 AM, Adrian Prantl <[email protected]> wrote:
>>>>>
>>>>> On Feb 27, 2013, at 11:31 AM, John McCall <[email protected]> wrote:
>>>>>> Okay, you're saying that the value is actually no longer live at all at
>>>>>> this point in the function? It seems reasonable to lose track of the
>>>>>> debug info then, although we should be leaving behind a marker in the
>>>>>> DWARF that says the value is unavailable.
>>>>>>
>>>>>> If we want to make stronger guarantees in -O0 for purposes of debugging
>>>>>> — and I think that's reasonable — then throwing the value in an alloca
>>>>>> is acceptable.
>>>>>
>>>>> To clarify: Are you suggesting to only generate the alloca at -O0, or are
>>>>> you comfortable with it as it is?
>>>>>
>>>>> If the value isn't live past that spot I'm more comfortable with dropping
>>>>> the debug info there rather than changing the generated code to keep the
>>>>> value live through the end of the function.
>>>>
>>>> Purely out of attachment to the principle that debug info shouldn't change
>>>> the code?
>>>>
>>>>
>>>> Pretty much.
>>>>
>>>> Not losing information has intrinsic value in a debug build. If we need
>>>> to emit slightly different code in order to force a value to stay live and
>>>> thus improve the debugging experience, then so be it.
>>>>
>>>>
>>>> Agreed that making the experience better is desirable, but it can make
>>>> debugging a problem more difficult if the code changes when you turn on
>>>> debugging symbols.
>>>
>>> Ah, I see your point; not doing the alloca could slide stack frames around.
>>>
>>> Alright, I agree with emitting it in all -O0 builds.
>>>
>>> Thought if optimization should fix it then perhaps all builds? :)
>>
>> I don't see any point in creating it just for mem2reg to trivially destroy.
>> :)
>>
>>> That said I'll remove the objection to the allocas. We'll need to fix the
>>> alloca problem at some point, but making poor Adrian do it right now for
>>> this bug when we've got other workarounds already in the source base seems
>>> a bit mean.
>>
>> Well, if the value really isn't live anymore, then I'm not sure what the
>> supposed alloca problem is, other than needing to leave breadcrumbs to say
>> that the value isn't available at this point in the function. We definitely
>> don't want regalloc to be keeping values live just for debug info!
>
> FYI: this is what the patch looks like if output the alloca only at -O0.
+ if (CGM.getCodeGenOpts().OptimizationLevel == 0)
+ blockAddr = Builder.CreateLoad(blockAddr);
No. The kind of value in LocalDeclMap should not vary according to
target optimization level.
What you should do is:
- under -O0, always emit an alloca for the block context parameter and store
the block context into it, and
- under -g, tie the debug info the block context parameter to the alloca, if it
exists, and otherwise to the raw argument value.
+ if (CGM.getCodeGenOpts().OptimizationLevel == 0) {
+ llvm::Value *selfAddr =
Don't do this. If you need to re-indent, re-indent.
+// RUN: %clang_cc1 %s -O0 -fblocks -triple x86_64-apple-darwin -emit-llvm -o -
| FileCheck %s
I'm confused, because that's the default.
+// RUN: %clang -fblocks -S -g -fverbose-asm -triple x86_64-apple-darwin -o -
%s | FileCheck %s
Like Eric mentioned, tests that need to check backend output shouldn't go
in the clang test suite. Change the test to check IR output or move it to
LLVM.
John.
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