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Diffstat (limited to 'docs/BranchWeightMetadata.rst')
| -rw-r--r-- | docs/BranchWeightMetadata.rst | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/docs/BranchWeightMetadata.rst b/docs/BranchWeightMetadata.rst index 9e61d232d74b..b941d0d15050 100644 --- a/docs/BranchWeightMetadata.rst +++ b/docs/BranchWeightMetadata.rst @@ -123,11 +123,11 @@ To allow comparing different functions during inter-procedural analysis and optimization, ``MD_prof`` nodes can also be assigned to a function definition. The first operand is a string indicating the name of the associated counter. -Currently, one counter is supported: "function_entry_count". This is a 64-bit -counter that indicates the number of times that this function was invoked (in -the case of instrumentation-based profiles). In the case of sampling-based -profiles, this counter is an approximation of how many times the function was -invoked. +Currently, one counter is supported: "function_entry_count". The second operand +is a 64-bit counter that indicates the number of times that this function was +invoked (in the case of instrumentation-based profiles). In the case of +sampling-based profiles, this operand is an approximation of how many times +the function was invoked. For example, in the code below, the instrumentation for function foo() indicates that it was called 2,590 times at runtime. @@ -138,3 +138,13 @@ indicates that it was called 2,590 times at runtime. ret i32 0 } !1 = !{!"function_entry_count", i64 2590} + +If "function_entry_count" has more than 2 operands, the later operands are +the GUID of the functions that needs to be imported by ThinLTO. This is only +set by sampling based profile. It is needed because the sampling based profile +was collected on a binary that had already imported and inlined these functions, +and we need to ensure the IR matches in the ThinLTO backends for profile +annotation. The reason why we cannot annotate this on the callsite is that it +can only goes down 1 level in the call chain. For the cases where +foo_in_a_cc()->bar_in_b_cc()->baz_in_c_cc(), we will need to go down 2 levels +in the call chain to import both bar_in_b_cc and baz_in_c_cc. |