spirv: Handle OpBranchConditional with the same lables

Yevhenii Kolesnikov requested to merge GL/mesa:fix/3786_same_condition_v2 into main

Consider CFG of this code:

      %B5 = OpLabel
            OpSelectionMerge %B8 None
            OpBranchConditional %true %B6 %B6
      %B6 = OpLabel
            OpBranchConditional %true %B7 %B8
      %B7 = OpLabel
            OpBranch %B8
      %B8 = OpLabel


In this case, after processing %B5, we want to jump to its merge node, %B8. So we can't just treat conditional branches with the same labels as unconditional.

In the presence of a merge node, we preserve this construct in a form of vtn_if with only then branch set up. We get rid of it later in vtn_emit_cf_list_structured.

Signed-off-by: Yevhenii Kolesnikov yevhenii.kolesnikov@globallogic.com Closes: #3786 (closed)

Edited by Yevhenii Kolesnikov

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