[llvm] Add PreLegalizer pattern matching for degrees GL extension (PR #216506)

[Matt Arsenault via llvm-commits]

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@@ -22,6 +22,12 @@ def vector_select_to_faceforward_lowering : GICombineRule <
   (apply [{ Helper.applySPIRVFaceForward(*${root}); }])
 >;
 
+def degrees_lowering
+    : GICombineRule<(defs root:$root),
+                    (match (wip_match_opcode G_FMUL):$root,
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arsenm wrote:

avoid adding new uses of wip_match_opcode 

https://github.com/llvm/llvm-project/pull/216506