Update CFGWalker to generate consolidated exit blocks #6079
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Previously CFGWalker designated a particular block as the "exit" block, but it was just the block that happened to appear at the end of the function that returned values by implicitly flowing them out. That exit block was not tied in any way to other blocks that might end in returns, so analyses that needed to perform some action at the end of the function would have had to perform that action at the end of the designated exit block but also separately at any return instruction. Update CFGWalker to make the exit block a synthetic empty block that is a successor of all other blocks tthat implicitly or explicitly return from the function in case there are multiple such blocks, or to make the exit block the single returning block if there is only one. This means that analyses will only perform their end-of-function actions at the end of the exit block rather than additionally at every return instruction.
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Current dependencies on/for this PR:
This stack of pull requests is managed by Graphite. |
This was referenced Nov 4, 2023
kripken
approved these changes
Nov 6, 2023
src/cfg/cfg-traversal.h
Outdated
| // The exit block for the function: either the single block that returns or | ||
| // flows values out of the function, or an empty synthetic block that is a | ||
| // successor of all such blocks. This block may not exist if a function | ||
| // traps or infinitely loops and therefore never exits. |
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Might be worth mentioning throwing here, which is not considered an "exit". That is, the exit is the "return to caller, possibly with a value" block, not a general "exit from function somehow" block (which would have included exceptions).
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I confirmed that this does not change performance on --merge-locals, which uses local graph. |
radekdoulik
pushed a commit
to dotnet/binaryen
that referenced
this pull request
Jul 12, 2024
Previously CFGWalker designated a particular block as the "exit" block, but it was just the block that happened to appear at the end of the function that returned values by implicitly flowing them out. That exit block was not tied in any way to other blocks that might end in returns, so analyses that needed to perform some action at the end of the function would have had to perform that action at the end of the designated exit block but also separately at any return instruction. Update CFGWalker to make the exit block a synthetic empty block that is a successor of all other blocks tthat implicitly or explicitly return from the function in case there are multiple such blocks, or to make the exit block the single returning block if there is only one. This means that analyses will only perform their end-of-function actions at the end of the exit block rather than additionally at every return instruction.
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Previously CFGWalker designated a particular block as the "exit" block, but it
was just the block that happened to appear at the end of the function that
returned values by implicitly flowing them out. That exit block was not tied in
any way to other blocks that might end in returns, so analyses that needed to
perform some action at the end of the function would have had to perform that
action at the end of the designated exit block but also separately at any return
instruction.
Update CFGWalker to make the exit block a synthetic empty block that is a
successor of all other blocks that implicitly or explicitly return from the
function in case there are multiple such blocks, or to make the exit block the
single returning block if there is only one. This means that analyses will only
perform their end-of-function actions at the end of the exit block rather than
additionally at every return instruction.