[llvm-commits] [llvm] r68950 - /llvm/trunk/lib/Target/X86/X86Instr64bit.td

[Dan Gohman]

Author: djg
Date: Mon Apr 13 10:13:28 2009
New Revision: 68950

URL: http://llvm.org/viewvc/llvm-project?rev=68950&view=rev
Log:
Add a comment about MOVSX64rr8.

Modified:
    llvm/trunk/lib/Target/X86/X86Instr64bit.td

Modified: llvm/trunk/lib/Target/X86/X86Instr64bit.td
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86Instr64bit.td?rev=68950&r1=68949&r2=68950&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/X86Instr64bit.td (original)
+++ llvm/trunk/lib/Target/X86/X86Instr64bit.td Mon Apr 13 10:13:28 2009
@@ -255,6 +255,10 @@
 
 // Sign/Zero extenders
 
+// MOVSX64rr8 always has a REX prefix and it has an 8-bit register
+// operand, which makes it a rare instruction with an 8-bit register
+// operand that can never access an h register. If support for h registers
+// were generalized, this would require a special register class.
 def MOVSX64rr8 : RI<0xBE, MRMSrcReg, (outs GR64:$dst), (ins GR8 :$src),
                     "movs{bq|x}\t{$src, $dst|$dst, $src}",
                     [(set GR64:$dst, (sext GR8:$src))]>, TB;