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target-indep codegen memcpy lowering issue.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47705 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-02-28 05:34:27 +00:00
parent daf6c541b2
commit 48840f8db9
1 changed files with 44 additions and 0 deletions
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lib/Target/README.txt
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@ -628,3 +628,47 @@ to know that it doesn't modify G either. This is very tricky.
We should add an FRINT node to the DAG to model targets that have legal
implementations of ceil/floor/rint.
//===---------------------------------------------------------------------===//
Consider:
int test() {
long long input[8] = {1,1,1,1,1,1,1,1};
foo(input);
}
We currently compile this into a memcpy from a global array since the
initializer is fairly large and not memset'able. This is good, but the memcpy
gets lowered to load/stores in the code generator. This is also ok, except
that the codegen lowering for memcpy doesn't handle the case when the source
is a constant global. This gives us atrocious code like this:
call "L1$pb"
"L1$pb":
popl %eax
movl _C.0.1444-"L1$pb"+32(%eax), %ecx
movl %ecx, 40(%esp)
movl _C.0.1444-"L1$pb"+20(%eax), %ecx
movl %ecx, 28(%esp)
movl _C.0.1444-"L1$pb"+36(%eax), %ecx
movl %ecx, 44(%esp)
movl _C.0.1444-"L1$pb"+44(%eax), %ecx
movl %ecx, 52(%esp)
movl _C.0.1444-"L1$pb"+40(%eax), %ecx
movl %ecx, 48(%esp)
movl _C.0.1444-"L1$pb"+12(%eax), %ecx
movl %ecx, 20(%esp)
movl _C.0.1444-"L1$pb"+4(%eax), %ecx
...
instead of:
movl $1, 16(%esp)
movl $0, 20(%esp)
movl $1, 24(%esp)
movl $0, 28(%esp)
movl $1, 32(%esp)
movl $0, 36(%esp)
...
//===---------------------------------------------------------------------===//