[llvm-commits] [llvm] r72396 - /llvm/trunk/lib/Target/X86/README.txt

[Chris Lattner]

Author: lattner
Date: Mon May 25 15:28:19 2009
New Revision: 72396

URL: http://llvm.org/viewvc/llvm-project?rev=72396&view=rev
Log:
add some late optimizations that GCC does.  It thinks these are a win
even on Core2, not just AMD processors which was a surprise to me.

Modified:
    llvm/trunk/lib/Target/X86/README.txt

Modified: llvm/trunk/lib/Target/X86/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README.txt?rev=72396&r1=72395&r2=72396&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/README.txt (original)
+++ llvm/trunk/lib/Target/X86/README.txt Mon May 25 15:28:19 2009
@@ -1883,3 +1883,17 @@
 fall back to lower-granularity chunks.
 
 //===---------------------------------------------------------------------===//
+
+Implement processor-specific optimizations for parity with GCC on these
+processors.  GCC does two optimizations:
+
+1. ix86_pad_returns inserts a noop before ret instructions if immediately
+   preceeded by a conditional branch or is the target of a jump.
+2. ix86_avoid_jump_misspredicts inserts noops in cases where a 16-byte block of
+   code contains more than 3 branches.
+   
+The first one is done for all AMDs, Core2, and "Generic"
+The second one is done for: Atom, Pentium Pro, all AMDs, Pentium 4, Nocona,
+  Core 2, and "Generic"
+
+//===---------------------------------------------------------------------===//