Coalesce duplicate spills and reloads per CFG block#2892
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milan-tom merged 29 commits intooxcaml:mainfrom Aug 14, 2024
Merged
Coalesce duplicate spills and reloads per CFG block#2892milan-tom merged 29 commits intooxcaml:mainfrom
milan-tom merged 29 commits intooxcaml:mainfrom
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xclerc
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(I have not read 96afa85 yet.) |
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xclerc
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TheNumbat
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LGTM, Xavier's comments already cover my thoughts
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xclerc
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Completed final checks and confirmed changes when optimization is disabled are only in files modified in this PR. |
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At present, if register allocation fails to register allocate a variable it is reloaded/spilled from the stack for every use throughout the duration of the whole program (either via creation of a new temporary register for that use or direct use in an instruction if the architecture supports this). This creates situations where even in a single CFG block the same variable may be reloaded and spilled many times. This can be avoided by using a register for that variable for the duration of a single block. This PR aims to do this by optimising the temporaries created after the first round of register allocation (only for this round to avoid infinite loops and the more rounds this optimisation is involved in the longer register allocation takes) to ensure at most one temporary register is used per variable in each CFG block.
Analysis of improvement (tested on compiler files)
Files
Functions
NB: Timing information is not analysed here as the files in the compiler are too small to do meaningful analyses of the worst cases.
The files/functions that have worse counts afterwards are due to assigning block temporaries for variables which have live ranges across a block that interfere with other registers which have already been register allocated. Future PR(s) will address this by disabling/tweaking the optimization in this case.
Full analysis (preview below)
