Ok for vector_shuffle mask to contain undef elements.

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

diff --git a/lib/Target/PowerPC/README.txt b/lib/Target/PowerPC/README.txt
index 42a644c1f33cf2df19a3e9c28d8c9892f4198df4..14a0bc124ed7f42bfa1374f323615426675535ef 100644 (file)
--- a/lib/Target/PowerPC/README.txt
+++ b/lib/Target/PowerPC/README.txt
@@ -1,3 +1,5 @@
+//===- README.txt - Notes for improving PowerPC-specific code gen ---------===//
+
 TODO:
 * gpr0 allocation
 * implement do-loop -> bdnz transform
@@ -309,12 +311,6 @@ Generate lwbrx and other byteswapping load/store instructions when reasonable.
 
 ===-------------------------------------------------------------------------===
 
-Implement TargetConstantVec, and set up PPC to custom lower ConstantVec into
-TargetConstantVec's if it's one of the many forms that are algorithmically
-computable using the spiffy altivec instructions.
-
-===-------------------------------------------------------------------------===
-
 Compile this:
 
 int foo(int a) {
@@ -502,11 +498,6 @@ This theoretically may help improve twolf slightly (used in dimbox.c:142?).
 
 ===-------------------------------------------------------------------------===
 
-Implement PPCInstrInfo::isLoadFromStackSlot/isStoreToStackSlot for vector
-registers, to generate better spill code.
-
-===-------------------------------------------------------------------------===
-
 int foo(int N, int ***W, int **TK, int X) {
   int t, i;
   
@@ -519,20 +510,44 @@ int foo(int N, int ***W, int **TK, int X) {
 
 We generate relatively atrocious code for this loop compared to gcc.
 
+We could also strength reduce the rem and the div:
+http://www.lcs.mit.edu/pubs/pdf/MIT-LCS-TM-600.pdf
+
 ===-------------------------------------------------------------------------===
 
-Altivec support.  The first should be a single lvx from the constant pool, the
-second should be a xor/stvx:
+float foo(float X) { return (int)(X); }
 
-void foo(void) {
-  int x[8] __attribute__((aligned(128))) = { 1, 1, 1, 1, 1, 1, 1, 1 };
-  bar (x);
-}
+Currently produces:
 
-#include <string.h>
-void foo(void) {
-  int x[8] __attribute__((aligned(128)));
-  memset (x, 0, sizeof (x));
-  bar (x);
+_foo:
+        fctiwz f0, f1
+        stfd f0, -8(r1)
+        lwz r2, -4(r1)
+        extsw r2, r2
+        std r2, -16(r1)
+        lfd f0, -16(r1)
+        fcfid f0, f0
+        frsp f1, f0
+        blr
+
+We could use a target dag combine to turn the lwz/extsw into an lwa when the 
+lwz has a single use.  Since LWA is cracked anyway, this would be a codesize
+win only.
+
+===-------------------------------------------------------------------------===
+
+We generate ugly code for this:
+
+void func(unsigned int *ret, float dx, float dy, float dz, float dw) {
+  unsigned code = 0;
+  if(dx < -dw) code |= 1;
+  if(dx > dw)  code |= 2;
+  if(dy < -dw) code |= 4;
+  if(dy > dw)  code |= 8;
+  if(dz < -dw) code |= 16;
+  if(dz > dw)  code |= 32;
+  *ret = code;
 }
 
+===-------------------------------------------------------------------------===
+