[llvm] r273868 - Add an explanation on how mips is special in here.

[Rafael Espindola via llvm-commits]

Author: rafael
Date: Mon Jun 27 07:33:33 2016
New Revision: 273868

URL: http://llvm.org/viewvc/llvm-project?rev=273868&view=rev
Log:
Add an explanation on how mips is special in here.

Modified:
    llvm/trunk/lib/Target/Mips/MipsISelLowering.cpp

Modified: llvm/trunk/lib/Target/Mips/MipsISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Mips/MipsISelLowering.cpp?rev=273868&r1=273867&r2=273868&view=diff
==============================================================================
--- llvm/trunk/lib/Target/Mips/MipsISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/Mips/MipsISelLowering.cpp Mon Jun 27 07:33:33 2016
@@ -1764,6 +1764,17 @@ SDValue MipsTargetLowering::lowerGlobalA
     return getAddrNonPIC(N, SDLoc(N), Ty, DAG);
   }
 
+  // Every other architecture would use shouldAssumeDSOLocal in here, but
+  // mips is special.
+  // * In PIC code mips requires got loads oven for local statics!
+  // * To save on got entries, for local statics the got entry contains the
+  //   page and an additional add instruction takes care of the low bits.
+  // * It is legal to access a hidden symbol with a non hidden undefined,
+  //   so one cannot guarantee that all access to a hidden symbol will know
+  //   it is hidden.
+  // * Mips linkers don't support creating a page and a full got entry for
+  //   the same symbol.
+  // * Given all that, we have to use a full got entry for hidden symbols :-(
   if (GV->hasLocalLinkage())
     return getAddrLocal(N, SDLoc(N), Ty, DAG, ABI.IsN32() || ABI.IsN64());