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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90428 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-12-03 07:41:54 +00:00
parent 93e0ed31c5
commit 053321731c
1 changed files with 32 additions and 0 deletions
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32
lib/Target/README.txt
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@ -1704,3 +1704,35 @@ need all but the bottom two bits from %A, and if we gave that mask to SDB it
would delete the or instruction for us.
//===---------------------------------------------------------------------===//
FunctionAttrs is not marking this function as readnone (just readonly):
$ clang t.c -emit-llvm -S -o - -O0 | opt -mem2reg -S -functionattrs
int t(int a, int b, int c) {
int *p;
if (a)
p = &a;
else
p = &c;
return *p;
}
This is because we codegen this to:
define i32 @t(i32 %a, i32 %b, i32 %c) nounwind readonly ssp {
entry:
%a.addr = alloca i32 ; <i32*> [#uses=3]
%c.addr = alloca i32 ; <i32*> [#uses=2]
...
if.end:
%p.0 = phi i32* [ %a.addr, %if.then ], [ %c.addr, %if.else ]
%tmp2 = load i32* %p.0 ; <i32> [#uses=1]
ret i32 %tmp2
}
And functionattrs doesn't realize that the p.0 load points to function local
memory.
//===---------------------------------------------------------------------===//