Author: lattner
Date: Wed Dec 5 17:05:06 2007
New Revision: 44638
URL: http://llvm.org/viewvc/llvm-project?rev=44638&view=rev
Log:
add a note
Modified:
llvm/trunk/lib/Target/README.txt
Modified: llvm/trunk/lib/Target/README.txt
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=44638&r1=44637&r2=44638&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Wed Dec 5 17:05:06 2007
@@ -463,5 +463,42 @@
ret int %tmp3
}
+//===---------------------------------------------------------------------===//
+on this code:
+unsigned array[4];
+unsigned foo(unsigned long x) {
+ return array[(x>>2)&3ul];
+}
+
+we should dag combine the left+right shift together. We currently get:
+
+_foo:
+ movl 4(%esp), %eax
+ shrl $2, %eax
+ andl $3, %eax
+ movl _array(,%eax,4), %eax
+ ret
+
+similar on ppc:
+
+_foo:
+ lis r2, ha16(_array)
+ srwi r3, r3, 2
+ la r2, lo16(_array)(r2)
+ rlwinm r3, r3, 2, 28, 29
+ lwzx r3, r2, r3
+ blr
+
+similar on arm:
+
+_foo:
+ mov r3, #3
+ and r3, r3, r0, lsr #2
+ ldr r2, LCPI1_0
+ ldr r0, [r2, +r3, lsl #2]
+ bx lr
+
+this is a trivial dag combine xform.
+//===---------------------------------------------------------------------===//
_______________________________________________
llvm-commits mailing list
llvm-commits@cs.uiuc.edu
http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
