[llvm-commits] [PATCH, PR-13709]: Remove unnecessary SRL instruction to access high sub-reg of a register pair.

[Pranav Bhandarkar]

Hi,

This is a fix for PR13709.

We peephole optimize by forwarding the high-subreg of a register pair, Rp0
into the copy of the lower subregister of Rp1 in 

""
Rp1 = SRL Rp0, 32
Rx = Rp1: subreg_loreg
""

So, we transform the above into.
"""
Rp1 = SRL Rp0, 32   // dead if there are no other uses of Rp1.
Rx = Rp0:subreg_hireg
"""

Built and Installed fine. No regressions on make check.

Pranav
Qualcomm Innovation Center (QuIC) is a member of the Code Aurora Forum.
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