Changes in directory llvm/lib/Target/PowerPC:
README.txt updated: 1.69 -> 1.70
---
Log message:
add a note
---
Diffs of the changes: (+41 -0)
README.txt | 41 +++++++++++++++++++++++++++++++++++++++++
1 files changed, 41 insertions(+)
Index: llvm/lib/Target/PowerPC/README.txt
diff -u llvm/lib/Target/PowerPC/README.txt:1.69
llvm/lib/Target/PowerPC/README.txt:1.70
--- llvm/lib/Target/PowerPC/README.txt:1.69 Mon Mar 6 22:42:59 2006
+++ llvm/lib/Target/PowerPC/README.txt Tue Mar 7 18:25:47 2006
@@ -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?).
+
+===-------------------------------------------------------------------------===
+
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