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 898af148e0adc4fe856ca186095ecc3d90203260..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
@@ -10,13 +12,8 @@ still a codesize win.
 
 ===-------------------------------------------------------------------------===
 
-Should hint to the branch select pass that it doesn't need to print the second
-unconditional branch, so we don't end up with things like:
-       b .LBBl42__2E_expand_function_8_674     ; loopentry.24
-       b .LBBl42__2E_expand_function_8_42      ; NewDefault
-       b .LBBl42__2E_expand_function_8_42      ; NewDefault
-
-This occurs in SPASS.
+Teach the .td file to pattern match PPC::BR_COND to appropriate bc variant, so
+we don't have to always run the branch selector for small functions.
 
 ===-------------------------------------------------------------------------===
 
@@ -314,12 +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) {
@@ -507,3 +498,56 @@ This theoretically may help improve twolf slightly (used in dimbox.c:142?).
 
 ===-------------------------------------------------------------------------===
 
+int foo(int N, int ***W, int **TK, int X) {
+  int t, i;
+  
+  for (t = 0; t < N; ++t)
+    for (i = 0; i < 4; ++i)
+      W[t / X][i][t % X] = TK[i][t];
+      
+  return 5;
+}
+
+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
+
+===-------------------------------------------------------------------------===
+
+float foo(float X) { return (int)(X); }
+
+Currently produces:
+
+_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;
+}
+
+===-------------------------------------------------------------------------===
+