[docs] Improvements to CMake.rst

[oota-llvm.git] / docs / BranchWeightMetadata.rst

diff --git a/docs/BranchWeightMetadata.rst b/docs/BranchWeightMetadata.rst
index f0df971f8745c7e2227a289e6a9aab8acebb3e8f..2ebc6c32416eaf2281d58b4f6cb3e2348a1cc008 100644 (file)
--- a/docs/BranchWeightMetadata.rst
+++ b/docs/BranchWeightMetadata.rst
@@ -1,5 +1,3 @@
-.. _branch_weight:
-
 ===========================
 LLVM Branch Weight Metadata
 ===========================
@@ -10,10 +8,11 @@ LLVM Branch Weight Metadata
 Introduction
 ============
 
-Branch Weight Metadata represents branch weights as its likeliness to be
-taken. Metadata is assigned to the ``TerminatorInst`` as a ``MDNode`` of the
-``MD_prof`` kind. The first operator is always a ``MDString`` node with the
-string "branch_weights". Number of operators depends on the terminator type.
+Branch Weight Metadata represents branch weights as its likeliness to be taken
+(see :doc:`BlockFrequencyTerminology`). Metadata is assigned to the
+``TerminatorInst`` as a ``MDNode`` of the ``MD_prof`` kind. The first operator
+is always a ``MDString`` node with the string "branch_weights".  Number of
+operators depends on the terminator type.
 
 Branch weights might be fetch from the profiling file, or generated based on
 `__builtin_expect`_ instruction.
@@ -27,8 +26,8 @@ Supported Instructions
 ``BranchInst``
 ^^^^^^^^^^^^^^
 
-Metadata is only assign to the conditional branches. There are two extra
-operarands, for the true and the false branch.
+Metadata is only assigned to the conditional branches. There are two extra
+operarands for the true and the false branch.
 
 .. code-block:: llvm
 
@@ -41,8 +40,8 @@ operarands, for the true and the false branch.
 ``SwitchInst``
 ^^^^^^^^^^^^^^
 
-Branch weights are assign to every case (including ``default`` case which is
-always case #0).
+Branch weights are assigned to every case (including the ``default`` case which
+is always case #0).
 
 .. code-block:: llvm
 
@@ -55,7 +54,7 @@ always case #0).
 ``IndirectBrInst``
 ^^^^^^^^^^^^^^^^^^
 
-Branch weights are assign to every destination.
+Branch weights are assigned to every destination.
 
 .. code-block:: llvm
 
@@ -116,3 +115,26 @@ CFG Modifications
 Branch Weight Metatada is not proof against CFG changes. If terminator operands'
 are changed some action should be taken. In other case some misoptimizations may
 occur due to incorrent branch prediction information.
+
+Function Entry Counts
+=====================
+
+To allow comparing different functions durint 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.
+
+For example, in the code below, the instrumentation for function foo()
+indicates that it was called 2,590 times at runtime.
+
+.. code-block:: llvm
+
+  define i32 @foo() !prof !1 {
+    ret i32 0
+  }
+  !1 = !{!"function_entry_count", i64 2590}