Clarify the difference between ISD::BITCAST and the bitcast instruction from LLVM-IR.

[dsanders]

Hi,

I just found this patch which I must have forgotten about. Is it ok to commit?

[dsanders]

Thanks

From: James Molloy [mailto:[e-mail]]
Sent: 09 May 2016 16:50
To: [e-mail]; Daniel Sanders
Cc: [e-mail]
Subject: Re: [PATCH] D16464: Clarify the difference between ISD::BITCAST and the bitcast instruction from LLVM-IR.

Hi,

It looks good to me.

James

include/llvm/CodeGen/ISDOpcodes.h

enum NodeType {
 
     /// BITCAST - This operator converts between integer, vector and FP
     /// values, as if the value was stored to memory with one type and loaded
     /// from the same address with the other type (or equivalently for vector
     /// format conversions, etc).  The source and result are required to have
     /// the same bit size (e.g.  f32 <-> i32).  This can also be used for
     /// int-to-int or fp-to-fp conversions, but that is a noop, deleted by
     /// getNode().
+    ///
+    /// This operator is subtly different from the bitcast instruction from
+    /// LLVM-IR since this node may change the bits in the register. For
+    /// example, this occurs on big-endian NEON and big-endian MSA where the
+    /// layout of the bits in the register depends on the vector type and this
+    /// operator acts as a shuffle operation for some vector type combinations.
     BITCAST,
 
     /// ADDRSPACECAST - This operator converts between pointers of different
     /// address spaces.
     ADDRSPACECAST,
 
     /// CONVERT_RNDSAT - This operator is used to support various conversions
     /// between various types (float, signed, unsigned and vectors of those