[llvm] [SelectionDAG] Fix assertion failure on inline asm register type mismatch (PR #166615)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,20 @@
+; RUN: not llc -mtriple=x86_64-unknown-linux-gnu < %s 2>&1 | FileCheck %s
+
+; Test that using MMX register constraint 'y' (64-bit) with a 256-bit vector
+; produces a proper error message instead of an assertion failure.
+
+; CHECK: error: couldn't allocate output register for constraint 'y'
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arsenm wrote:

This isn't the tested error message 

https://github.com/llvm/llvm-project/pull/166615