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

[Chris Lattner]

Changes in directory llvm/lib/Target:

README.txt updated: 1.48 -> 1.49
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Log message:

add a note


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Diffs of the changes:  (+16 -0)

 README.txt |   16 ++++++++++++++++
 1 files changed, 16 insertions(+)


Index: llvm/lib/Target/README.txt
diff -u llvm/lib/Target/README.txt:1.48 llvm/lib/Target/README.txt:1.49
--- llvm/lib/Target/README.txt:1.48	Sun Nov 12 18:23:28 2006
+++ llvm/lib/Target/README.txt	Mon Nov 13 19:57:53 2006
@@ -16,6 +16,22 @@
 
 //===---------------------------------------------------------------------===//
 
+With the recent changes to make the implicit def/use set explicit in
+machineinstrs, we should change the target descriptions for 'call' instructions
+so that the .td files don't list all the call-clobbered registers as implicit
+defs.  Instead, these should be added by the code generator (e.g. on the dag).
+
+This has a number of uses:
+
+1. PPC32/64 and X86 32/64 can avoid having multiple copies of call instructions
+   for their different impdef sets.
+2. Targets with multiple calling convs (e.g. x86) which have different clobber
+   sets don't need copies of call instructions.
+3. 'Interprocedural register allocation' can be done to reduce the clobber sets
+   of calls.
+
+//===---------------------------------------------------------------------===//
+
 FreeBench/mason contains code like this:
 
 static p_type m0u(p_type p) {