Changes in directory llvm/lib/Target/PowerPC:
README.txt updated: 1.68 -> 1.69
---
Log message:
add a note
---
Diffs of the changes: (+14 -0)
README.txt | 14 ++++++++++++++
1 files changed, 14 insertions(+)
Index: llvm/lib/Target/PowerPC/README.txt
diff -u llvm/lib/Target/PowerPC/README.txt:1.68
llvm/lib/Target/PowerPC/README.txt:1.69
--- llvm/lib/Target/PowerPC/README.txt:1.68 Wed Mar 1 00:36:20 2006
+++ llvm/lib/Target/PowerPC/README.txt Mon Mar 6 22:42:59 2006
@@ -452,3 +452,17 @@
srwi r3, r2, 24
blr
+===-------------------------------------------------------------------------===
+
+On the G5, logical CR operations are more expensive in their three
+address form: ops that read/write the same register are half as expensive as
+those that read from two registers that are different from their destination.
+
+We should model this with two separate instructions. The isel should generate
+the "two address" form of the instructions. When the register allocator
+detects that it needs to insert a copy due to the two-addresness of the CR
+logical op, it will invoke PPCInstrInfo::convertToThreeAddress. At this point
+we can convert to the "three address" instruction, to save code space.
+
+This only matters when we start generating cr logical ops.
+
_______________________________________________
llvm-commits mailing list
[email protected]
http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
