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days of trying to figure it out. Despite some developer's penchant for
relaxing the tool versions, this just isn't possible. Only certain versions
work with certain other versions.

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Patch contributed by Paolo Invernizzi

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to go in.  This patch allows us to compute the trip count of loops controlled
by values loaded from constant arrays.  The cannonnical example of this is
strlen when passed a constant argument:

for (int i = 0; "constantstring"[i]; ++i) ;
return i;

In this case, it will compute that the loop executes 14 times, which means
that the exit value of i is 14.  Because of this, the loop gets DCE'd and
we are happy.  This also applies to anything that does similar things, e.g.
loops like this:

  const float Array[] = { 0.1, 2.1, 3.2, 23.21 };
  for (int i = 0; Array[i] < 20; ++i)

and is actually fairly general.

The problem with this is that it almost never triggers.  The reason is that
we run indvars and the loop optimizer only at compile time, which is before
things like strlen and strcpy have been inlined into the program from libc.
Because of this, it almost never is used (it triggers twice in specint2k).

I'm committing it because it DOES work, may be useful in the future, and
doesn't slow us down at all.  If/when we start running the loop optimizer
at link-time (-O4?) this will be very nice indeed :)

llvm-svn: 16926

marker from one ilist into the middle of another basic block!

llvm-svn: 16925

pointer recurrences into expressions from this:

  %P_addr.0.i.0 = phi sbyte* [ getelementptr ([8 x sbyte]* %.str_1, int 0, int 0), %entry ], [ %inc.0.i, %no_exit.i ]
  %inc.0.i = getelementptr sbyte* %P_addr.0.i.0, int 1            ; <sbyte*> [#uses=2]

into this:

  %inc.0.i = getelementptr sbyte* getelementptr ([8 x sbyte]* %.str_1, int 0, int 0), int %inc.0.i.rec

Actually create something nice, like this:

  %inc.0.i = getelementptr [8 x sbyte]* %.str_1, int 0, int %inc.0.i.rec

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well as a vector of constant*'s.  It turns out that this is more efficient
and all of the clients want to do that, so we should cater to them.

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First, it allows SRA of globals that have embedded arrays, implementing
GlobalOpt/globalsra-partial.llx.  This comes up infrequently, but does allow,
for example, deleting several stores to dead parts of globals in dhrystone.

Second, this implements GlobalOpt/malloc-promote-*.llx, which is the
following nifty transformation:

Basically if a global pointer is initialized with malloc, and we can tell
that the program won't notice, we transform this:

struct foo *FooPtr;
...
  FooPtr = malloc(sizeof(struct foo));
...
  FooPtr->A   FooPtr->B

Into:

struct foo FooPtrBody;
...
   FooPtrBody.A  FooPtrBody.B

This comes up occasionally, for example, the 'disp' global in 183.equake (where
the xform speeds the CBE version of the program up from 56.16s to 52.40s (7%)
on apoc), and the 'desired_accept', 'fixLRBT', 'macroArray', & 'key_queue'
globals in 300.twolf (speeding it up from 22.29s to 21.55s (3.4%)).

The nice thing about this xform is that it exposes the resulting global to
global variable optimization and makes alias analysis easier in addition to
eliminating a few loads.

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cannot be SRA'd

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cases.

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first element of an array, return a GEP instead of a cast.  This allows us
to transparently fold this:

int* getelementptr (int* cast ([100 x int]* %Gbody to int*), int 40)

into this:

int* getelementptr ([100 x int]* %Gbody, int 0, int 40)

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