diff --git a/lib/Target/X86/X86InstrInfo.cpp b/lib/Target/X86/X86InstrInfo.cpp
index 6d2bf1d4969..c81ddb19003 100644
--- a/lib/Target/X86/X86InstrInfo.cpp
+++ b/lib/Target/X86/X86InstrInfo.cpp
@@ -12,8 +12,11 @@
 // descriptors
 //
 static const MachineInstrDescriptor X86Insts[] = {
-#define I(ENUM, NAME, FLAGS, TSFLAGS) \
-             { NAME, -1, -1, 0, false, 0, 0, TSFLAGS, FLAGS },
+#define I(ENUM, NAME, FLAGS, TSFLAGS)   \
+             { NAME,                    \
+               -1, /* Always vararg */  \
+               ((TSFLAGS) & X86II::Void) ? -1 : 0,  /* Result is in 0 */ \
+               0, false, 0, 0, TSFLAGS, FLAGS, TSFLAGS },
 #include "X86InstrInfo.def"
 };
 
diff --git a/lib/Target/X86/X86InstrInfo.def b/lib/Target/X86/X86InstrInfo.def
index bd4e47be4d3..2388b9bf38d 100644
--- a/lib/Target/X86/X86InstrInfo.def
+++ b/lib/Target/X86/X86InstrInfo.def
@@ -5,6 +5,10 @@
 // specified below, and is used to make all of the information relevant to an
 // instruction be in one place.
 //
+// Note that X86 Instructions always have the destination register listed as
+// operand 0, unless it does not produce a value (in which case the TSFlags will
+// include X86II::Void).
+//
 //===----------------------------------------------------------------------===//
 
 // NOTE: No include guards desired