NarrowScalar G_SMULH in LegalizerHelper using MultiplyRegisters helper function.
NarrowScalar G_SMULH for MIPS32.
We need to wait for NarrowScalar of G_SEXT and G_ZEXT and for perfecting artifact legalization
(since here it depends in which order we attempt to combine artifacts that are chained).
Could you rebase the patch?
Join declaration and initialization.
Addressed review comments.
Needs a test. This may need the -gisel-abort=0 trick to hack around the artifact issues
I added this patch to show how we can handle G_SMULH in narrowScalarMul, will add the test in the future.