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add a deadargelim note.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90009 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-11-27 17:12:30 +00:00
parent 6d94926a52
commit 1d159838a3
1 changed files with 23 additions and 0 deletions
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23
lib/Target/README.txt
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@ -2,6 +2,29 @@ Target Independent Opportunities:
//===---------------------------------------------------------------------===//
Dead argument elimination should be enhanced to handle cases when an argument is
dead to an externally visible function. Though the argument can't be removed
from the externally visible function, the caller doesn't need to pass it in.
For example in this testcase:
void foo(int X) __attribute__((noinline));
void foo(int X) { sideeffect(); }
void bar(int A) { foo(A+1); }
We compile bar to:
define void @bar(i32 %A) nounwind ssp {
%0 = add nsw i32 %A, 1 ; <i32> [#uses=1]
tail call void @foo(i32 %0) nounwind noinline ssp
ret void
}
The add is dead, we could pass in 'i32 undef' instead. This occurs for C++
templates etc, which usually have linkonce_odr/weak_odr linkage, not internal
linkage.
//===---------------------------------------------------------------------===//
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