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[bitmanip][WiP] [RFC] Add automatic generation of pack*#267
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rdolbeau wants to merge 1 commit intoriscvarchive:riscv-gcc-10.2.0-rvbfrom
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[bitmanip][WiP] [RFC] Add automatic generation of pack*#267rdolbeau wants to merge 1 commit intoriscvarchive:riscv-gcc-10.2.0-rvbfrom
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This adds automatic generation of pack* instructions (pack, packu, packh) beyond zero-extension. This is implemented via a custom pass that a) reorganize chains of '[ix]or' to exhibit regular patterns; b) matches common pattern of pack/packu/packh and replace them by the appropriate instruction
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This adds automatic generation of pack* instructions (pack, packu, packh) beyond zero-extension.
This is implemented via a custom pass that
a) reorganize chains of '[ix]or' to exhibit regular patterns;
b) matches common pattern of pack/packu/packh and replace them by the appropriate instruction
(as the code is very different, this PR draft replaces #262)
Not sure if it's completely suitable, but it should help quantify how useful those instructions are on a given code.
For instance, in openssl 1.1.1k on
rv32gcbk_zbr_zbt, the compiler reorganize 470 sequences of three[ix]orand produces 1125packhand 682pack(plus some more that are matched directly). Many (most?) of them seems to be related to byte-by-byte loading of 32 bits words (lbu/lbu/lbu/lbu/packh/packh/pack). If the addresses were provably aligned they could be replaced by the much more efficientlw/grevi 0x18, but it's difficult to achieve in the back-end - the source code should probably be changed to use an explicit load-word/byte-reversal when using a 32-bits load is legal. For comparison, the resulting objects (all.oin thedirectory collectively contain (the source was patched to implement an AES with scalarK, hence theaes32*):[edit] Adding a source file showing some of the patterns that match (or don't in some cases)
pack-pattern.txt