SHUFP* are two address code.

[oota-llvm.git] / lib / Target / README.txt

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index a28486091cbc459c4b9037ecd6c86bd35bf3bb2b..c2635dade4181062bd96f3476b220837dbc71afd 100644 (file)
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -17,7 +17,11 @@ We currently compile this into a memcpy from a static array into 'm', then
 a bunch of loads from m.  It would be better to avoid the memcpy and just do
 loads from the static array.
 
-===-------------------------------------------------------------------------===
+//===---------------------------------------------------------------------===//
+
+Make the PPC branch selector target independant
+
+//===---------------------------------------------------------------------===//
 
 Get the C front-end to expand hypot(x,y) -> llvm.sqrt(x*x+y*y) when errno and
 precision don't matter (ffastmath).  Misc/mandel will like this. :)
@@ -54,6 +58,9 @@ There are two ways to fix this:
 
 Number 1 is the preferred solution.
 
+This has been "fixed" by a TableGen hack. But that is a short term workaround
+which will be removed once the proper fix is made.
+
 //===---------------------------------------------------------------------===//
 
 Turn this into a signed shift right in instcombine:
@@ -85,16 +92,6 @@ Shrink: (setlt (loadi32 P), 0) -> (setlt (loadi8 Phi), 0)
 
 //===---------------------------------------------------------------------===//
 
-Reassociate is missing this:
-
-int test(int X, int Y) {
- return (X+X+Y+Y);  // (X+Y) << 1;
-}
-
-it needs to turn the shifts into multiplies to get it.
-
-//===---------------------------------------------------------------------===//
-
 Reassociate should turn: X*X*X*X -> t=(X*X) (t*t) to eliminate a multiply.
 
 //===---------------------------------------------------------------------===//
@@ -120,3 +117,24 @@ for 1,2,4,8 bytes.
 
 //===---------------------------------------------------------------------===//
 
+This code:
+int rot(unsigned char b) { int a = ((b>>1) ^ (b<<7)) & 0xff; return a; }
+
+Can be improved in two ways:
+
+1. The instcombiner should eliminate the type conversions.
+2. The X86 backend should turn this into a rotate by one bit.
+
+//===---------------------------------------------------------------------===//
+
+Add LSR exit value substitution. It'll probably be a win for Ackermann, etc.
+
+//===---------------------------------------------------------------------===//
+
+It would be nice to revert this patch:
+http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20060213/031986.html
+
+And teach the dag combiner enough to simplify the code expanded before 
+legalize.  It seems plausible that this knowledge would let it simplify other
+stuff too.
+