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update and consolidate the load pre notes.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90050 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2009-11-29 02:19:52 +00:00
parent ff0a883fe9
commit d4137f40da
1 changed files with 40 additions and 41 deletions
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lib/Target/README.txt
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@ -1116,6 +1116,8 @@ later.
//===---------------------------------------------------------------------===//
[STORE SINKING]
Store sinking: This code:
void f (int n, int *cond, int *res) {
@ -1171,6 +1173,8 @@ This is GCC PR38204.
//===---------------------------------------------------------------------===//
[STORE SINKING]
GCC PR37810 is an interesting case where we should sink load/store reload
into the if block and outside the loop, so we don't reload/store it on the
non-call path.
@ -1198,7 +1202,7 @@ we don't sink the store. We need partially dead store sinking.
//===---------------------------------------------------------------------===//
[LOAD PRE with NON-AVAILABLE ADDRESS]
[LOAD PRE CRIT EDGE SPLITTING]
GCC PR37166: Sinking of loads prevents SROA'ing the "g" struct on the stack
leading to excess stack traffic. This could be handled by GVN with some crazy
@ -1217,63 +1221,58 @@ bb3: ; preds = %bb1, %bb2, %bb
%11 is partially redundant, an in BB2 it should have the value %8.
GCC PR33344 is a similar case.
GCC PR33344 and PR35287 are similar cases.
//===---------------------------------------------------------------------===//
[LOAD PRE]
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
GCC testsuite, ones we don't get yet are (checked through loadpre25):
[CRIT EDGE BREAKING]
loadpre3.c predcom-4.c
[PRE OF READONLY CALL]
loadpre5.c
[TURN SELECT INTO BRANCH]
loadpre14.c loadpre15.c
actually a conditional increment: loadpre18.c loadpre19.c
//===---------------------------------------------------------------------===//
[SCALAR PRE]
There are many PRE testcases in testsuite/gcc.dg/tree-ssa/ssa-pre-*.c in the
GCC testsuite.
//===---------------------------------------------------------------------===//
There are some interesting cases in testsuite/gcc.dg/tree-ssa/pred-comm* in the
GCC testsuite. For example, predcom-1.c is:
GCC testsuite. For example, we get the first example in predcom-1.c, but
miss the second one:
for (i = 2; i < 1000; i++)
fib[i] = (fib[i-1] + fib[i - 2]) & 0xffff;
unsigned fib[1000];
unsigned avg[1000];
which compiles into:
__attribute__ ((noinline))
void count_averages(int n) {
int i;
for (i = 1; i < n; i++)
avg[i] = (((unsigned long) fib[i - 1] + fib[i] + fib[i + 1]) / 3) & 0xffff;
}
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
which compiles into two loads instead of one in the loop.
This is basically:
LOAD fib[i+1]
LOAD fib[i]
STORE fib[i+2]
predcom-2.c is the same as predcom-1.c
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:
@ -1305,7 +1304,7 @@ 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
we miss it because we need 1) CRIT EDGE 2) MULTIPLE DIFFERENT
VALS PRODUCED BY ONE BLOCK OVER DIFFERENT PATHS
//===---------------------------------------------------------------------===//