Add Zcb extension#1025
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This commit is a cherry-pick of only the Zcb extension from Jonathan Jonssons's commit: 5e72708 Zcb (code reduction): since no gcc support is in the mainline assembler yet these instructions are injected as raw data. Coverage class has been extended with these instructions and the illegal instruction class should not be able to generate legal Zcb instruction if the extension is enabled. load_store_instr_lib: Added the Zcb load and store instructions to this class. Co-authored-by: Samuel Riedel <sriedel@lowrisc.org>"
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This PR adds support for the Zcb extension. It is originally derived from @JJ-Gaisler's commit in PR #921 but was split off to isolate the Zcb implementation for easier reviewing. It also cleans up a few existing nits and simplifies the
rdspecial cases.Therefore, this PR depends on PR #1024 and should be rebased and merged after that PR lands. Because Zcb introduces instructions requiring
rs1 == rd, having PR #1024 merged first simplifies the design. New changes from this PR: review only new commitsThose tests are used in Ibex's verification: lowRISC/ibex#2324