[llvm-commits] CVS: llvm/lib/Target/PowerPC/README.txt

[Chris Lattner]

Changes in directory llvm/lib/Target/PowerPC:

README.txt updated: 1.110 -> 1.111
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Log message:

add a note


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Diffs of the changes:  (+29 -0)

 README.txt |   29 +++++++++++++++++++++++++++++
 1 files changed, 29 insertions(+)


Index: llvm/lib/Target/PowerPC/README.txt
diff -u llvm/lib/Target/PowerPC/README.txt:1.110 llvm/lib/Target/PowerPC/README.txt:1.111
--- llvm/lib/Target/PowerPC/README.txt:1.110	Thu Feb  8 22:19:54 2007
+++ llvm/lib/Target/PowerPC/README.txt	Fri Feb  9 11:38:01 2007
@@ -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
+
+===-------------------------------------------------------------------------===