[llvm] r287710 - Before sample pgo annotation, do not inline a function that has no debug info. (NFC)

Mon Nov 28 14:32:29 PST 2016

On Mon, Nov 28, 2016 at 2:18 PM Dehao Chen <dehao at google.com> wrote:

> I thought NFC applies to "obvious change to fix corner-case bugs", and
> apparently I was wrong and I'm sorry about that.
>

Ah, right - NFC means No Functional Change. We use this to tag pure
refactoring changes that do not change the observable behavior of the
component in question. (eg: changing the API of SmallVector might not
change the observable behavior of LLVM, but it probably still wouldn't be
tagged NFC, because we tend to unit test ADTs directly - but changing some
pass so that it still optimizes in the same way, but doesn't, say, build
some intermediate data structure anymore, would be NFC because at the level
we test that pass, nothing has changed)

> What's the recommend steps to move forward for situations like this? Shall
> I revert the patch and send out a code review?
>

Doesn't seem like there's anything needed to be done - just an FYI of don't
use 'NFC' when semantics/behavior do change. You included what appears to
be appropriate test coverage, etc, so no worries there.

>
> On Mon, Nov 28, 2016 at 10:04 AM, David Blaikie <dblaikie at gmail.com>
> wrote:
>
>
>
> On Tue, Nov 22, 2016 at 2:59 PM Dehao Chen via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
> Author: dehao
> Date: Tue Nov 22 16:50:01 2016
> New Revision: 287710
>
> URL: http://llvm.org/viewvc/llvm-project?rev=287710&view=rev
> Log:
> Before sample pgo annotation, do not inline a function that has no debug
> info. (NFC)
>
>
> (+1 to Paul's comment - this sounds like a change, has test changes, and
> is probably not NFC)
>
> Also: This sounds like it does the opposite of what we want as a
> requirement: that the presence or absence of debug info should not change
> the resulting code.
>
> What's the deal?
>
>
> This particular pass requires debug info to make decisions.
>

Sorry, clearly not my area of understanding/expertise - could you give a
brief description of why/how that is?

> This is mandated by pass manager: even with -g0, PM will make sure debug
> info is available before this pass.
>

The PM doesn't produce debug info, though - the client building IR (Clang,
etc) does.

> But if user manually removed the debug info, the code should also handle
> it correctly, which is fixed by this patch.
>
> Dehao
>
>
>
>
>
> If there is no debug info in the callee, inlining it will not help
> annotator. This avoids infinite loop as reported in PR/31119.
>
> Added:
>     llvm/trunk/test/Transforms/SampleProfile/Inputs/nodebug.prof
>     llvm/trunk/test/Transforms/SampleProfile/nodebug.ll
> Modified:
>     llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp
>     llvm/trunk/test/Transforms/SampleProfile/early-inline.ll
>
> Modified: llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp?rev=287710&r1=287709&r2=287710&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp (original)
> +++ llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp Tue Nov 22 16:50:01
> 2016
> @@ -651,6 +651,8 @@ bool SampleProfileLoader::inlineHotFunct
>        InvokeInst *II = dyn_cast<InvokeInst>(I);
>        Function *CalledFunction =
>            (CI == nullptr ? II->getCalledFunction() :
> CI->getCalledFunction());
> +      if (!CalledFunction || !CalledFunction->getSubprogram())
> +        continue;
>        DebugLoc DLoc = I->getDebugLoc();
>        uint64_t NumSamples =
> findCalleeFunctionSamples(*I)->getTotalSamples();
>        if ((CI && InlineFunction(CI, IFI)) || (II && InlineFunction(II,
> IFI))) {
>
> Added: llvm/trunk/test/Transforms/SampleProfile/Inputs/nodebug.prof
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SampleProfile/Inputs/nodebug.prof?rev=287710&view=auto
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/SampleProfile/Inputs/nodebug.prof (added)
> +++ llvm/trunk/test/Transforms/SampleProfile/Inputs/nodebug.prof Tue Nov
> 22 16:50:01 2016
> @@ -0,0 +1,2 @@
> +foo:100:10
> + 0: bar:10
>
> Modified: llvm/trunk/test/Transforms/SampleProfile/early-inline.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SampleProfile/early-inline.ll?rev=287710&r1=287709&r2=287710&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/SampleProfile/early-inline.ll (original)
> +++ llvm/trunk/test/Transforms/SampleProfile/early-inline.ll Tue Nov 22
> 16:50:01 2016
> @@ -28,7 +28,7 @@ define void @_Z3foov() #0 personality i8
>  }
>
>  ; Function Attrs: nounwind uwtable
> -define internal void @_ZL3barv() #1 {
> +define internal void @_ZL3barv() !dbg !12 {
>    ret void
>  }
>
> @@ -45,3 +45,4 @@ declare i32 @__gxx_personality_v0(...)
>  !9 = !DILocation(line: 6, column: 3, scope: !6)
>  !10 = !DILocation(line: 8, column: 5, scope: !11)
>  !11 = distinct !DILexicalBlock(scope: !6, file: !1, line: 7, column: 7)
> +!12 = distinct !DISubprogram(linkageName: "_ZL3barv", scope: !1, line:
> 20, scopeLine: 20, unit: !0)
>
> Added: llvm/trunk/test/Transforms/SampleProfile/nodebug.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SampleProfile/nodebug.ll?rev=287710&view=auto
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/SampleProfile/nodebug.ll (added)
> +++ llvm/trunk/test/Transforms/SampleProfile/nodebug.ll Tue Nov 22
> 16:50:01 2016
> @@ -0,0 +1,20 @@
> +; RUN: opt < %s -sample-profile
> -sample-profile-file=%S/Inputs/nodebug.prof
> +
> +define void @foo() !dbg !3 {
> +  call void @bar(), !dbg !4
> +  ret void
> +}
> +
> +define void @bar() {
> +  call void @bar()
> +  ret void
> +}
> +
> +!llvm.dbg.cu = !{!0}
> +!llvm.module.flags = !{!2}
> +
> +!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1)
> +!1 = !DIFile(filename: "t", directory: "/tmp/")
> +!2 = !{i32 2, !"Debug Info Version", i32 3}
> +!3 = distinct !DISubprogram(name: "a", scope: !1, file: !1, line: 10,
> unit: !0)
> +!4 = !DILocation(line: 10, scope: !3)
>
>
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