[PATCH] D61472: [X86FixupLEAs] Turn optIncDec into a generic two address LEA optimizer. Support LEA64_32r properly.

[Craig Topper via Phabricator via cfe-commits]

craig.topper added a comment.

In D61472#1515994 <https://reviews.llvm.org/D61472#1515994>, @spatel wrote:

> I haven't looked closely at the series of transforms that gets us here, so let me ask: would it be more efficient to produce the add/inc/dec machine instructions directly rather than LEA? Or do we do this because the 3-address opportunity helps register allocation, so this late reversal is a special-case of the more generally useful transforms that produce LEA in the 1st place?


I believe a lot of these are caused TwoAddressInstructionPass converting to three address sometimes when it maybe shouldn't. I think there's some overlap with the test diffs in D52109 <https://reviews.llvm.org/D52109>. But I don't think the change I made in that diff is correct. There appear to be some test changes here that aren't affected by that patch either. So maybe there are other issues in TwoAddressInstruction heuristics.


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https://reviews.llvm.org/D61472