[llvm] [AMDGPU] Optimize image sample followed by llvm.amdgcn.cvt.pkrtz into d16 variant (PR #145203)

[Harrison Hao via llvm-commits]

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@@ -247,6 +247,42 @@ simplifyAMDGCNImageIntrinsic(const GCNSubtarget *ST,
                                        ArgTys[0] = User->getType();
                                      });
         }
+
+        // Fold image.sample + cvt.pkrtz -> extractelement idx0 into a single
+        // d16 image sample.
----------------
harrisonGPU wrote:

So do you mean that if the input data is in fixed-point format, it gets converted to fp32 using RTE, and then if we use pkrtz, it applies RTZ?

If we fold this into a D16 image sample, it will only apply RTZ, which could cause accuracy issues. Is that what you're saying?

But in the IR I can't see any data format info in the image instruction, and I haven’t found a case that clearly uses a fixed-point format.

Do you have an example? I'd like to verify it. By fixed-point formats, you mean things like UNORM, right?

https://github.com/llvm/llvm-project/pull/145203