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llvm-svn: 61033
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Chris Lattner 2008-12-15 08:32:28 +00:00
parent 8119a1f70d
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lib/Target/README.txt
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@ -1354,12 +1354,58 @@ GCC PR33344 is a similar case.
There are many load PRE testcases in testsuite/gcc.dg/tree-ssa/loadpre* in the
GCC testsuite. There are many pre testcases as ssa-pre-*.c
//===---------------------------------------------------------------------===//
There are some interesting cases in testsuite/gcc.dg/tree-ssa/pred-comm* in the
GCC testsuite. For example, predcom-1.c is:
for (i = 2; i < 1000; i++)
fib[i] = (fib[i-1] + fib[i - 2]) & 0xffff;
which compiles into:
bb1: ; preds = %bb1, %bb1.thread
%indvar = phi i32 [ 0, %bb1.thread ], [ %0, %bb1 ]
%i.0.reg2mem.0 = add i32 %indvar, 2
%0 = add i32 %indvar, 1 ; <i32> [#uses=3]
%1 = getelementptr [1000 x i32]* @fib, i32 0, i32 %0
%2 = load i32* %1, align 4 ; <i32> [#uses=1]
%3 = getelementptr [1000 x i32]* @fib, i32 0, i32 %indvar
%4 = load i32* %3, align 4 ; <i32> [#uses=1]
%5 = add i32 %4, %2 ; <i32> [#uses=1]
%6 = and i32 %5, 65535 ; <i32> [#uses=1]
%7 = getelementptr [1000 x i32]* @fib, i32 0, i32 %i.0.reg2mem.0
store i32 %6, i32* %7, align 4
%exitcond = icmp eq i32 %0, 998 ; <i1> [#uses=1]
br i1 %exitcond, label %return, label %bb1
This is basically:
LOAD fib[i+1]
LOAD fib[i]
STORE fib[i+2]
instead of handling this as a loop or other xform, all we'd need to do is teach
load PRE to phi translate the %0 add (i+1) into the predecessor as (i'+1+1) =
(i'+2) (where i' is the previous iteration of i). This would find the store
which feeds it.
predcom-2.c is apparently the same as predcom-1.c
predcom-3.c is very similar but needs loads feeding each other instead of
store->load.
predcom-4.c seems the same as the rest.
//===---------------------------------------------------------------------===//
Other simple load PRE cases:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35287 [LPRE crit edge splitting]
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34677 (licm does this, LPRE crit edge)
llvm-gcc t2.c -S -o - -O0 -emit-llvm | llvm-as | opt -mem2reg -simplifycfg -gvn | llvm-dis
//===---------------------------------------------------------------------===//
Type based alias analysis:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705
//===---------------------------------------------------------------------===//
@ -1380,7 +1426,7 @@ int foo(int C, int *P, float X) {
One example (that requires crazy phi translation) is:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16799
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16799 [BITCAST PHI TRANS]
//===---------------------------------------------------------------------===//
@ -1388,9 +1434,14 @@ A/B get pinned to the stack because we turn an if/then into a select instead
of PRE'ing the load/store. This may be fixable in instcombine:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37892
Interesting missed case because of control flow flattening (should be 2 loads):
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26629
With: llvm-gcc t2.c -S -o - -O0 -emit-llvm | llvm-as |
opt -mem2reg -gvn -instcombine | llvm-dis
we miss it because we need 1) GEP PHI TRAN, 2) CRIT EDGE 3) MULTIPLE DIFFERENT
VALS PRODUCED BY ONE BLOCK OVER DIFFERENT PATHS
//===---------------------------------------------------------------------===//