[llvm] r353129 - [SamplePGO][NFC] Minor improvement to replace a temporary vector with a

[Richard Smith via llvm-commits]

Hi,

On Mon, 4 Feb 2019 at 16:57, Wei Mi via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: wmi
> Date: Mon Feb  4 16:57:50 2019
> New Revision: 353129
>
> URL: http://llvm.org/viewvc/llvm-project?rev=353129&view=rev
> Log:
> [SamplePGO][NFC] Minor improvement to replace a temporary vector with a
> brace-enclosed init list.
>
> Differential Revision: https://reviews.llvm.org/D57726
>
> Modified:
>     llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp
>
> Modified: llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp?rev=353129&r1=353128&r2=353129&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp (original)
> +++ llvm/trunk/lib/Transforms/IPO/SampleProfile.cpp Mon Feb  4 16:57:50 2019
> @@ -1327,9 +1327,8 @@ void SampleProfileLoader::propagateWeigh
>                              SortedCallTargets, Sum, IPVK_IndirectCallTarget,
>                              SortedCallTargets.size());
>          } else if (!dyn_cast<IntrinsicInst>(&I)) {
> -          SmallVector<uint32_t, 1> Weights;
> -          Weights.push_back(BlockWeights[BB]);
> -          I.setMetadata(LLVMContext::MD_prof, MDB.createBranchWeights(Weights));
> +          I.setMetadata(LLVMContext::MD_prof,
> +                        MDB.createBranchWeights({BlockWeights[BB]}));

This breaks the build with:

lib/Transforms/IPO/SampleProfile.cpp:1331:50: error:
non-constant-expression cannot be narrowed from type 'unsigned long'
to 'unsigned int' in initializer list [-Wc++11-narrowing]
                        MDB.createBranchWeights({BlockWeights[BB]}));
                                                 ^~~~~~~~~~~~~~~~
lib/Transforms/IPO/SampleProfile.cpp:1331:50: note: insert an explicit
cast to silence this issue
                        MDB.createBranchWeights({BlockWeights[BB]}));
                                                 ^~~~~~~~~~~~~~~~
                                                 static_cast<unsigned int>( )

This looks like it might be a real bug: BlockWeights allows 64-bit
weights, whereas createBranchWeights only allows 32-bit weights, so
there might be data loss here.

>          }
>        }
>      }
>
>
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