[llvm] [SPIRV] Add support for `bfloat16` atomics via the `SPV_INTEL_16bit_atomics` extension (PR #166257)

[Nathan Gauër via llvm-commits]

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@@ -1081,11 +1088,21 @@ static void AddAtomicFloatRequirements(const MachineInstr &MI,
     Reqs.addExtension(SPIRV::Extension::SPV_EXT_shader_atomic_float_add);
     switch (BitWidth) {
     case 16:
-      if (!ST.canUseExtension(
-              SPIRV::Extension::SPV_EXT_shader_atomic_float16_add))
-        report_fatal_error(ATOM_FLT_REQ_EXT_MSG("16_add"), false);
-      Reqs.addExtension(SPIRV::Extension::SPV_EXT_shader_atomic_float16_add);
-      Reqs.addCapability(SPIRV::Capability::AtomicFloat16AddEXT);
+      if (isBFloat16Type(TypeDef)) {
+        if (!ST.canUseExtension(SPIRV::Extension::SPV_INTEL_16bit_atomics))
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Keenuts wrote:

IIRC there is a later mechanism which checks which extension is allowed for the current target and raises an "SPIR-V module cannot be satisfied" error if an extension/capability is showing but is not allowed.

https://github.com/llvm/llvm-project/pull/166257