[llvm] [clang] [PowerPC] Implement fence builtin (PR #76495)

[Chen Zheng via llvm-commits]

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@@ -944,6 +944,9 @@ TARGET_BUILTIN(__builtin_pack_vector_int128, "V1LLLiULLiULLi", "", "vsx")
 // Set the floating point rounding mode
 BUILTIN(__builtin_setrnd, "di", "")
 
+// Barrier for instruction motion
+BUILTIN(__builtin_ppc_fence, "v", "")
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chenzheng1030 wrote:

nit: maybe we can put this builtin around line 100, together with other XL Compatibility built-ins.

https://github.com/llvm/llvm-project/pull/76495