[PATCH] D109889: AMDGPU: Broadcast scalar boolean to vector boolean explicitly

[Alexander via Phabricator via llvm-commits]

alex-t added a comment.

> Overall I think we should not have contexts where copy from SCC is being used as a broadcast to a vector boolean. I think these only arise as a side effect of the hacky way SIFixSGPRCopies rewrites the function instruction at a time

In the case given as an example - yes. As soon as I finish divergence-driven isel for the ISD::SELECT, this will turn to the following:

  s_addc_u32 s4, s6, 0
  s_cselect_b32 s4, s4, 0

But we still have other cases that are going to persist irrelative to the SIFixSGPRCopies hackery presence.

Ruiling gave me a good example in our last discussion on this topic:
What is about using the floating-point compare result in the bitwise operation?

  	s_cmp_ge_u32 s0, s1
  	s_cselect_b64 s[0:1], -1, 0
  	v_cmp_nlt_f32_e32 vcc, v1, v2
  	s_and_b64 vcc, vcc, s[0:1]
  	v_cndmask_b32_e32 v1, v2, v1, vcc

Both comparisons are uniform but we still have to broadcast SCC.


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https://reviews.llvm.org/D109889