[RISCV] Add test case to show a case where (mul (and X, 0xffffffff), (and Y, 0xffffffff)) optimization does not improve code.

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If the mul add two users, one of which was a sext.w, the mul
would also be selected to a MULW before our pattern runs. This
causes the ANDs to now be used by the already selected MULW and
the mul we still need to select. They are unneeded on the MULW
since MULW only reads the lower bits. So they get selected to
SLLI+SRLI for the MULW use. The use for the
(mul (and X, 0xffffffff), (and Y, 0xffffffff)) manages to reuse
the SLLI.

The end result is increased register pressure and no improvement
to how soon we can start the MULW.

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This commit is contained in:

Craig Topper 2021-03-20 17:43:30 -07:00

parent 361b7d125b

commit 27bc30c39d

1 changed files with 309 additions and 258 deletions

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llvm/test/CodeGen/RISCV/xaluo.ll

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