[llvm] [AMDGPU] ISel for @llvm.amdgcn.cs.chain intrinsic (PR #68186)

[Jay Foad via llvm-commits]

================
@@ -665,6 +665,50 @@ def : GCNPat<
   (SI_TCRETURN_GFX Gfx_CCR_SGPR_64:$src0, (i64 0), i32imm:$fpdiff)
 >;
 
+// Pseudo for the llvm.amdgcn.cs.chain intrinsic.
+// This is essentially a tail call, but it also takes a mask to put in EXEC
+// right before jumping to the callee.
+class SI_CS_CHAIN_TC<
+    ValueType execvt,
+    RegisterOperand execrc = !if(!eq(execvt, i32), SSrc_b32, SSrc_b64)>
----------------
jayfoad wrote:

Use `getSOPSrcForVT<...>.ret`?

https://github.com/llvm/llvm-project/pull/68186