[5.9] AllocStackHoisting: fix a quadratic complexity bug when merging stack locations. #68141
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… locations. Use consecutive instruction numbers to check for overlapping instead of iterating over the instruction list. This fixes a compile time problem which shows up if there are many stack locations in a large basic block. rdar://113207176
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airspeedswift
approved these changes
Aug 25, 2023
tomerd
approved these changes
Aug 25, 2023
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Explanation: This fixes a compile time problem which shows up if there are many stack locations in a large basic block. In the inner loop of the optimization the check for overlapping stack regions was done by iterating over all instructions of the basic block. The fix is to use consecutive instruction indices (which are stored in a map) to check for overlapping.
Issue: rdar://113207176
Risk: Low. The new overlapping check is done by 2 conditions which are 100% covered by the regression test.
Testing: With a regression test. Also, this optimization is so basic that it will be tested in nearly every program which is compiled.
Reviewer: @atrick
Main branch PR: AllocStackHoisting: fix a quadratic complexity bug when merging stack locations. #68139