[llvm] [AMDGPU] Fix MC/Disassembler/AMDGPU/decode-err.txt. (PR #96621)

[Jay Foad via llvm-commits]

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@@ -1,17 +1,18 @@
-# RUN: llvm-mc -triple=amdgcn -mcpu=gfx900 -disassemble -show-encoding < %s 2>&1 | FileCheck -check-prefix=GCN %s
-# RUN: llvm-mc -triple=amdgcn -mcpu=gfx1100 -disassemble -show-encoding < %s 2>&1 | FileCheck -check-prefixes=GFX11,W32 %s
-# RUN: llvm-mc -triple=amdgcn -mcpu=gfx1100 -mattr=-WavefrontSize32,+WavefrontSize64 -disassemble -show-encoding < %s 2>&1 | FileCheck -check-prefixes=GFX11,W64 %s
-# RUN: llvm-mc -triple=amdgcn -mcpu=gfx1200 -disassemble -show-encoding < %s 2>&1 | FileCheck -check-prefix=GFX12 %s
+# RUN: llvm-mc -triple=amdgcn -mcpu=gfx900 -disassemble -show-encoding -filetype=null < %s 2>&1 | FileCheck -check-prefix=GCN-ERR %s
+# RUN: llvm-mc -triple=amdgcn -mcpu=gfx1100 -disassemble -show-encoding < %s 2>&1 | FileCheck -check-prefixes=W32 %s
+# RUN: llvm-mc -triple=amdgcn -mcpu=gfx1100 -mattr=-WavefrontSize32,+WavefrontSize64 -disassemble -show-encoding < %s 2>&1 | FileCheck -check-prefixes=W64 %s
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jayfoad wrote:

> You also should never need to specify the negated form

@arsenm why do you say that? If you don't specify the negated form, you can end up with both wavefrontsize32 and wavefrontsize64 set, which is sometimes harmless but sometimes not. Related: #86957

https://github.com/llvm/llvm-project/pull/96621