[llvm] [LangRef] inline asm: the instructions are treated opaquely (PR #157080)

[Ralf Jung via llvm-commits]

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@@ -5229,6 +5229,11 @@ flag that indicates whether or not the inline asm expression has side effects,
 and a flag indicating whether the function containing the asm needs to align its
 stack conservatively.
 
+LLVM will treat the actual instructions entirely opaquely (i.e. no optimizations
+will be performed based on the contents of the template string). Only the flags,
+operand constraints, and attributes on the call and surrounding function are
+used to deduce what the expression may do during execution.
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RalfJung wrote:

That rules out the AMDGPU case of having magic comments in that string even more explicitly than before, I think.

I don't have a strong preference for whether that should be allowed or not, I am just trying to get some reasonable baseline documented. :) @nikic @arsenm do you have an opinion on this?

https://github.com/llvm/llvm-project/pull/157080