[llvm] [llvm-reduce] Use poison for x86_amx default constants (PR #218157)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,73 @@
+; RUN: llvm-reduce --delta-passes=instructions-to-return --test FileCheck --test-arg %s --test-arg --input-file %s
+
+; Check that we do not end up executing an unreachable by trying to create
+; a default constant value for an x86_amx value.
+
+; CHECK: x86_amx
+
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arsenm wrote:

Probably because instructions-to-returns is more complicated, and other special constant tests use operands-to-args. can you try basing this on the test from 37b5f77f8b145714d5931bb46ed090755376e179

https://github.com/llvm/llvm-project/pull/218157