add a note
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34101 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/README.txt b/lib/Target/PowerPC/README.txt
index a615b7e..932893e 100644
--- a/lib/Target/PowerPC/README.txt
+++ b/lib/Target/PowerPC/README.txt
@@ -596,3 +596,32 @@
This sort of thing occurs a lot due to globalopt.
===-------------------------------------------------------------------------===
+
+We currently compile 32-bit bswap:
+
+declare i32 @llvm.bswap.i32(i32 %A)
+define i32 @test(i32 %A) {
+ %B = call i32 @llvm.bswap.i32(i32 %A)
+ ret i32 %B
+}
+
+to:
+
+_test:
+ rlwinm r2, r3, 24, 16, 23
+ slwi r4, r3, 24
+ rlwimi r2, r3, 8, 24, 31
+ rlwimi r4, r3, 8, 8, 15
+ rlwimi r4, r2, 0, 16, 31
+ mr r3, r4
+ blr
+
+it would be more efficient to produce:
+
+_foo: mr r0,r3
+ rlwinm r3,r3,8,0xffffffff
+ rlwimi r3,r0,24,0,7
+ rlwimi r3,r0,24,16,23
+ blr
+
+===-------------------------------------------------------------------------===