add a note
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26605 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/README.txt b/lib/Target/PowerPC/README.txt
index 8fad506..898af14 100644
--- a/lib/Target/PowerPC/README.txt
+++ b/lib/Target/PowerPC/README.txt
@@ -466,3 +466,44 @@
This only matters when we start generating cr logical ops.
+===-------------------------------------------------------------------------===
+
+We should compile these two functions to the same thing:
+
+#include <stdlib.h>
+void f(int a, int b, int *P) {
+ *P = (a-b)>=0?(a-b):(b-a);
+}
+void g(int a, int b, int *P) {
+ *P = abs(a-b);
+}
+
+Further, they should compile to something better than:
+
+_g:
+ subf r2, r4, r3
+ subfic r3, r2, 0
+ cmpwi cr0, r2, -1
+ bgt cr0, LBB2_2 ; entry
+LBB2_1: ; entry
+ mr r2, r3
+LBB2_2: ; entry
+ stw r2, 0(r5)
+ blr
+
+GCC produces:
+
+_g:
+ subf r4,r4,r3
+ srawi r2,r4,31
+ xor r0,r2,r4
+ subf r0,r2,r0
+ stw r0,0(r5)
+ blr
+
+... which is much nicer.
+
+This theoretically may help improve twolf slightly (used in dimbox.c:142?).
+
+===-------------------------------------------------------------------------===
+