Add a note about a potential PIC optimization.

llvm-svn: 52663
2008-06-24 00:53:07 +00:00 · 2008-06-24 00:53:07 +00:00 · 02a2aaf2e7
parent 76600aa35c
commit 02a2aaf2e7
1 changed files with 7 additions and 0 deletions
--- a/llvm/lib/Target/X86/README.txt
+++ b/llvm/lib/Target/X86/README.txt
@ -1709,3 +1709,10 @@ _test:
 it would be better to codegen as: x+~y  (notl+addl)

 //===---------------------------------------------------------------------===//
+
+We should consider using __i686.get_pc_thunk.bx for MOVPC32r (used for PIC)
+on targets that support it, such as Linux and similar targets, in place of
+the call-a-label trick. It's said to be friendlier to branch-prediction
+hardware because it pairs a ret with the call.
+
+//===---------------------------------------------------------------------===//