[clang] [llvm] [NVPTX] Add ex2.approx bf16 support and cleanup intrinsic definition (PR #165446)

[Alex MacLean via cfe-commits]

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@@ -2550,6 +2554,11 @@ static Value *upgradeNVVMIntrinsicCall(StringRef Name, CallBase *CI,
     Intrinsic::ID IID = (Name == "fabs.ftz.f") ? Intrinsic::nvvm_fabs_ftz
                                                : Intrinsic::nvvm_fabs;
     Rep = Builder.CreateUnaryIntrinsic(IID, CI->getArgOperand(0));
+  } else if (Name.consume_front("ex2.approx.")) {
+    // nvvm.ex2.approx.{f,ftz.f,d,f16x2}
+    Intrinsic::ID IID = Name.starts_with("ftz") ? Intrinsic::nvvm_ex2_approx_ftz
+                                                : Intrinsic::nvvm_ex2_approx;
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AlexMaclean wrote:

This seems like too complex and potentially problematic a transformation to make in AutoUpgrade. We do similar transformations in `convertNvvmIntrinsicToLlvm` which is called during InstCombine, but I think we don't do this for "approx" intrinsics because the semantics don't match the llvm versions. 

https://github.com/llvm/llvm-project/pull/165446