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In testing, we've found yet another miscompile caused by the new tables. And this one is even less clear how to fix (we could teach it to fold a 16-bit load instead of the 32-bit load it wants, or block folding entirely). Also, the approach to excluding instructions seems increasingly to not scale well. I have left a more detailed analysis on the review log for the original patch (https://reviews.llvm.org/D32684) along with suggested path forward. I will land an additional test case that I wrote which covers the code that was miscompiling (folding into the output of `pextrw`) in a subsequent commit to keep this a pure revert. For each commit reverted here, I've restricted the revert to the non-test code touching the x86 fold table emission until the last commit where I did revert the test updates. This means the *new* test cases added for `insertps` and `xchg` remain untouched (and continue to pass). Reverted commits: r304540: [X86] Don't fold into memory operands into insertps in the ... r304347: [TableGen] Adapt more places to getValueAsString now ... r304163: [X86] Don't fold away the memory operand of an xchg. r304123: Don't capture a temporary std::string in a StringRef. r304122: Resubmit "[X86] Adding new LLVM TableGen backend that ..." Original commit was in r304088, and after a string of fixes was reverted previously in r304121 to fix build bots, and then re-landed in r304122. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304762 91177308-0d34-0410-b5e6-96231b3b80d8