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Add --x86-64-v2 and similar to configure - #1092
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This commit extends the approach here for flfma: 8f6a290 |
Valid levels are 1, 2, 3, and 4, but only 1 versus 2 and up matters currently. Confoguring for level 1 means that POPCOUNT and SSE4.1 instructions are used directly instead of linked dynamically when available.
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This is a follow-up to #1088, so it's a candidate for merging only after that PR, and only the most recent commit here is intended for the PR.
Add a
--x86-64-v<level>option toconfigureto control code generation for x86_64 extensions. The allowed<level>s are1through4. The configure flag is meant to be reminiscent of-march=x86-64-v2as a compiler flag, and the intent is to follow the meaning of levels 1 through 4 in the x86-64 psABI. Forbuild.bat, the flag is/x86-64-v<level>.Using
<level>as2causes POPCOUNT and SSE4.1 rounding instructions to be used directly in generated code, instead of added by linking only when available at run time (which imposes a small cost compared to directly using an instruction). A future change might use<level>as3to enable the FMA instruction.It could make sense for
--x86-64-v2to be a different machine type, instead of a option controllinga6(i.e., x86_64) targets. Making it a configuration choice withina6is less disruptive and seems more consistent with the way these kinds of architecture specializations are usually selected.Note that using
--x86-64-v2can make sense when usingconfigurefor a non-x86_64 platform if something likemake ta6le.bootis going to be used to generate boot files. (Most of the work in this PR was getting the build dependencies straight so that reconfiguring with a different level does that right thing in both cross and non-cross build modes.)