[TableGen] Fix prefix detection with anchor (NFC) #71379
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instregex uses an optimization, where the constant prefix of the regex is extracted to perform a binary search first. However, this optimization currently mainly fails to apply, because most instregex uses have an explicit ^ anchor, which gets counted as a meta char and disables the optimization. Make sure the anchor is skipped when determining the prefix. Also fix an implementation bug this exposes, where the pick a too long prefix if the first meta character is a quantifier. This cuts the time needed to generate files like X86GenInstrInfo.inc by half.
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zahiraam
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Nov 20, 2023
instregex uses an optimization, where the constant prefix of the regex is extracted to perform a binary search first. However, this optimization currently mainly fails to apply, because most instregex uses have an explicit ^ anchor, which gets counted as a meta char and disables the optimization. Make sure the anchor is skipped when determining the prefix. Also fix an implementation bug this exposes, where the pick a too long prefix if the first meta character is a quantifier. This cuts the time needed to generate files like X86GenInstrInfo.inc by half.
Guzhu-AMD
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Nov 23, 2023
Local branch amd-gfx 4810346 Merged main:01893b54835b into amd-gfx:d6fa9f734aa3 Remote branch main 0a0e06f [TableGen] Fix prefix detection with anchor (NFC) (llvm#71379)
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instregex uses an optimization, where the constant prefix of the regex is extracted to perform a binary search first. However, this optimization currently mainly fails to apply, because most instregex uses have an explicit ^ anchor, which gets counted as a meta char and disables the optimization.
Make sure the anchor is skipped when determining the prefix. Also fix an implementation bug this exposes, where the pick a too long prefix if the first meta character is a quantifier.
This cuts the time needed to generate files like X86GenInstrInfo.inc by half.