On Oct 13, 2009, Alexandre Oliva <aol...@redhat.com> wrote:
> On Jun 1, 2009, Alexandre Oliva <aol...@redhat.com> wrote:
>> A long time ago, when variable tracking at assignments was just a
>> distant dream, we ran into one of the first contentious points, which
>> had to do with coalescing SSA names on copyrename.
>> On the one hand, coalescing unrelated SSA names made for better code (at
>> least in theory) but poorer debug information; on the other hand,
>> refraining from coalescing them exploded compile-time memory use.
>> We currently implement a trade-off by which variables inlined from other
>> functions can be coalesced, so as to save compile-time memory, reduce
>> abstraction penalties and retain debug information for out-of-line
>> functions.
>> The patch below (ping) implements two other possibilities: refraining
>> from coalescing even inlined SSA names, which might enable better debug
>> information to be generated, and enabling coalescing of all related
>> variables, for better code at the expense of debug information.
>> VTA doesn't really care which of the 3 possibilities is used, it works
>> equally well with all of them.
> On Jun 1, 2009, Alexandre Oliva <aol...@redhat.com> also wrote:
>> And the patch below changes the default so that we can optimize more.
> This patch combines the two patches described above, now that VTA is
> enabled by default.
This is an updated version of the patch, adjusting the testcases that
didn't expect this kind of variable coalescing. Regstrapped on
x86_64-linux-gnu and i686-linux-gnu, along with a patch for a latent
cprop problem that caused a compare-debug failure in the ada rts.
Ok to install?
for gcc/ChangeLog
from Alexandre Oliva <aol...@redhat.com>
* common.opt (ftree-coalesce-inlined-vars): New.
(ftree-coalesce-vars): New.
* doc/invoke.texi: Document them.
* tree-ssa-copyrename.c (copy_rename_partition_coalesce):
Implement them.
for gcc/testsuite/ChangeLog
from Alexandre Oliva <aol...@redhat.com>
* g++.dg/tree-ssa/ivopts-2.C: Adjust for coalescing.
* gcc.dg/tree-ssa/forwprop-11.c: Likewise.
* gcc.dg/tree-ssa/ssa-fre-1.c: Likewise.
* gcc.dg/guality/bswaptest.c: Avoid coalescing and early death
of test variable.
* gcc.dg/guality/clztest.c: Likewise.
* gcc.dg/guality/ctztest.c: Likewise.
* gcc.dg/guality/rotatetest.c: Likewise.
Index: gcc/common.opt
===================================================================
--- gcc/common.opt.orig 2011-06-04 09:00:30.005102549 -0300
+++ gcc/common.opt 2011-06-04 09:01:29.199347556 -0300
@@ -1898,6 +1898,14 @@ ftree-ch
Common Report Var(flag_tree_ch) Optimization
Enable loop header copying on trees
+ftree-coalesce-inlined-vars
+Common Report Var(flag_ssa_coalesce_vars,1) Init(2) RejectNegative Optimization
+Enable coalescing of copy-related user variables that are inlined
+
+ftree-coalesce-vars
+Common Report Var(flag_ssa_coalesce_vars,2) Optimization
+Enable coalescing of all copy-related user variables
+
ftree-copyrename
Common Report Var(flag_tree_copyrename) Optimization
Replace SSA temporaries with better names in copies
Index: gcc/tree-ssa-copyrename.c
===================================================================
--- gcc/tree-ssa-copyrename.c.orig 2011-06-04 09:00:30.160103200 -0300
+++ gcc/tree-ssa-copyrename.c 2011-06-04 09:01:29.252347770 -0300
@@ -194,20 +194,21 @@ copy_rename_partition_coalesce (var_map
ign1 = TREE_CODE (root1) == VAR_DECL && DECL_IGNORED_P (root1);
ign2 = TREE_CODE (root2) == VAR_DECL && DECL_IGNORED_P (root2);
- /* Never attempt to coalesce 2 user variables unless one is an inline
- variable. */
+ /* Refrain from coalescing user variables, if requested. */
if (!ign1 && !ign2)
{
- if (DECL_FROM_INLINE (root2))
+ if (flag_ssa_coalesce_vars && DECL_FROM_INLINE (root2))
ign2 = true;
- else if (DECL_FROM_INLINE (root1))
+ else if (flag_ssa_coalesce_vars && DECL_FROM_INLINE (root1))
ign1 = true;
- else
+ else if (flag_ssa_coalesce_vars != 2)
{
if (debug)
fprintf (debug, " : 2 different USER vars. No coalesce.\n");
return false;
}
+ else
+ ign2 = true;
}
/* If both values have default defs, we can't coalesce. If only one has a
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi.orig 2011-06-04 09:00:30.665105322 -0300
+++ gcc/doc/invoke.texi 2011-06-04 09:01:29.479348698 -0300
@@ -395,8 +395,8 @@ Objective-C and Objective-C++ Dialects}.
-fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
-fsplit-wide-types -fstack-protector -fstack-protector-all @gol
-fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
--ftree-bit-ccp @gol
--ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
+-ftree-bit-ccp -ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol
+-ftree-coalesce-inline-vars -ftree-coalesce-vars -ftree-copy-prop @gol
-ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse @gol
-ftree-forwprop -ftree-fre -ftree-loop-if-convert @gol
-ftree-loop-if-convert-stores -ftree-loop-im @gol
@@ -7231,6 +7231,22 @@ temporaries to other variables at copy l
variable names which more closely resemble the original variables. This flag
is enabled by default at @option{-O} and higher.
+@item -ftree-coalesce-inlined-vars
+A more limited form of @option{-ftree-coalesce-vars}, that performs
+the transformation if at least one of the variables was inlined. This
+may harm debug information of such inlined variables, but it will keep
+variables of the main function apart from each other, such that they
+are more likely to contain the expected values in a debugging session.
+This was the default in GCC versions older than 4.7.
+
+@item -ftree-coalesce-vars
+Tell the compiler to attempt to combine small user variables that
+don't need to live in memory, when it finds a copy between them. This
+may severely limit the ability to debug an optimized program compiled
+without @option{-fvar-tracking-assignments}. In the negated form,
+this flag prevents SSA coalescing of user variables, including inlined
+ones. This option is enabled by default.
+
@item -ftree-ter
@opindex ftree-ter
Perform temporary expression replacement during the SSA->normal phase. Single
Index: gcc/testsuite/g++.dg/tree-ssa/ivopts-2.C
===================================================================
--- gcc/testsuite/g++.dg/tree-ssa/ivopts-2.C.orig 2011-06-04 09:13:29.613784393 -0300
+++ gcc/testsuite/g++.dg/tree-ssa/ivopts-2.C 2011-06-04 09:16:24.688235836 -0300
@@ -7,5 +7,5 @@ void test (int *b, int *e, int stride)
*p = 1;
}
-/* { dg-final { scan-tree-dump-times "PHI <p" 1 "ivopts"} } */
+/* { dg-final { scan-tree-dump-times "PHI <\[pb\]" 1 "ivopts"} } */
/* { dg-final { cleanup-tree-dump "ivopts" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/forwprop-11.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/forwprop-11.c.orig 2011-06-04 09:08:19.363853778 -0300
+++ gcc/testsuite/gcc.dg/tree-ssa/forwprop-11.c 2011-06-04 09:09:12.127024253 -0300
@@ -16,5 +16,5 @@ int g(int *p, int n)
return q[-1];
}
-/* { dg-final { scan-tree-dump-times "= MEM\\\[\\\(int \\\*\\\)a_.. \\\+ 4B\\\];" 2 "forwprop1" } } */
+/* { dg-final { scan-tree-dump-times "= MEM\\\[\\\(int \\\*\\\)\[ap\]_.. \\\+ 4B\\\];" 2 "forwprop1" } } */
/* { dg-final { cleanup-tree-dump "forwprop1" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-1.c.orig 2011-06-04 09:11:37.164466849 -0300
+++ gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-1.c 2011-06-04 09:11:41.365479111 -0300
@@ -11,5 +11,5 @@ int f(int *a)
return *c + t;
}
-/* { dg-final { scan-tree-dump "Replaced \\\*c_\[^\n\].*with t_" "fre1" } } */
+/* { dg-final { scan-tree-dump "Replaced \\\*\[ac\]_\[^\n\].*with t_" "fre1" } } */
/* { dg-final { cleanup-tree-dump "fre1" } } */
Index: gcc/testsuite/gcc.dg/guality/bswaptest.c
===================================================================
--- gcc/testsuite/gcc.dg/guality/bswaptest.c.orig 2011-06-04 09:35:38.954014890 -0300
+++ gcc/testsuite/gcc.dg/guality/bswaptest.c 2011-06-04 09:35:51.345054255 -0300
@@ -10,7 +10,7 @@ foo (long x)
long g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 12 "g" "f" } } */
- return f;
+ return f - g;
}
__attribute__((noclone, noinline)) int
@@ -20,7 +20,7 @@ bar (int x)
int g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 22 "g" "f" } } */
- return f;
+ return f - g;
}
int
Index: gcc/testsuite/gcc.dg/guality/clztest.c
===================================================================
--- gcc/testsuite/gcc.dg/guality/clztest.c.orig 2011-06-04 09:35:39.202015678 -0300
+++ gcc/testsuite/gcc.dg/guality/clztest.c 2011-06-04 09:36:17.710136856 -0300
@@ -10,7 +10,7 @@ foo (long x)
long g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 12 "g" "f" } } */
- return f;
+ return f - g;
}
__attribute__((noinline, noclone)) long
@@ -20,7 +20,7 @@ bar (long x)
long g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 22 "g" "f" } } */
- return f;
+ return f - g;
}
int
Index: gcc/testsuite/gcc.dg/guality/ctztest.c
===================================================================
--- gcc/testsuite/gcc.dg/guality/ctztest.c.orig 2011-06-04 09:35:39.463016509 -0300
+++ gcc/testsuite/gcc.dg/guality/ctztest.c 2011-06-04 09:36:33.143184587 -0300
@@ -10,7 +10,7 @@ foo (long x)
long g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 12 "g" "f" } } */
- return f;
+ return f - g;
}
__attribute__((noinline, noclone)) long
@@ -20,7 +20,7 @@ bar (long x)
long g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 22 "g" "f" } } */
- return f;
+ return f - g;
}
int
Index: gcc/testsuite/gcc.dg/guality/rotatetest.c
===================================================================
--- gcc/testsuite/gcc.dg/guality/rotatetest.c.orig 2011-06-04 09:32:07.155300180 -0300
+++ gcc/testsuite/gcc.dg/guality/rotatetest.c 2011-06-04 09:34:46.757846376 -0300
@@ -10,7 +10,7 @@ f1 (unsigned long x)
long g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 12 "g" "f" } } */
- return f;
+ return f - g;
}
__attribute__((noclone, noinline)) long
@@ -20,7 +20,7 @@ f2 (unsigned long x, int y)
long g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 22 "g" "f" } } */
- return f;
+ return f - g;
}
__attribute__((noclone, noinline)) long
@@ -30,7 +30,7 @@ f3 (unsigned long x, int y)
long g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 32 "g" "f" } } */
- return f;
+ return f - g;
}
__attribute__((noclone, noinline)) unsigned int
@@ -40,7 +40,7 @@ f4 (unsigned int x)
unsigned int g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 42 "g" "f" } } */
- return f;
+ return f - g;
}
__attribute__((noclone, noinline)) unsigned int
@@ -50,7 +50,7 @@ f5 (unsigned int x, int y)
unsigned int g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 52 "g" "f" } } */
- return f;
+ return f - g;
}
__attribute__((noclone, noinline)) unsigned int
@@ -60,7 +60,7 @@ f6 (unsigned int x, int y)
unsigned int g = f;
asm volatile ("" : "+r" (f));
vv++; /* { dg-final { gdb-test 62 "g" "f" } } */
- return f;
+ return f - g;
}
int
--
Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/ FSF Latin America board member
Free Software Evangelist Red Hat Brazil Compiler Engineer
