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| -rw-r--r-- | llvm/docs/LoopTerminology.rst | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/llvm/docs/LoopTerminology.rst b/llvm/docs/LoopTerminology.rst index 9eac6d71a6d..46aac1ebb95 100644 --- a/llvm/docs/LoopTerminology.rst +++ b/llvm/docs/LoopTerminology.rst @@ -80,18 +80,23 @@ Preheader Block - A preheader is a (singular) loop predecessor which ends in an unconditional transfer of control to the loop header. Note that not all loops have such blocks. -Backedge Taken Count - The number of times the backedge will have -executed before some interesting event happens. Commonly used without +Backedge Taken Count - The number of times the backedge will execute +before some interesting event happens. Commonly used without qualification of the event as a shorthand for when some exiting block branches to some exit block. May be zero, or not statically computable. -Iteration Count - The number of times the header has executed before -some interesting event happens. Commonly used w/o qualification to +Iteration Count - The number of times the header will execute before +some interesting event happens. Commonly used without qualification to refer to the iteration count at which the loop exits. Will always be -one greater than the backedge taken count. (Warning: Preceding +one greater than the backedge taken count. *Warning*: Preceding statement is true in the *integer domain*; if you're dealing with fixed width integers (such as LLVM Values or SCEVs), you need to be cautious -of overflow when converting one to the other.) +of overflow when converting one to the other. + +It's important to note that the same basic block can play multiple +roles in the same loop, or in different loops at once. For example, a +single block can be the header for two nested loops at once, while +also being an exit block for a sibling loop. Loop Simplify Form ================== |
