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Re: [PATCH] Improve ifcombine
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Richard Biener <rguenther at suse dot de>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Wed, 12 Mar 2014 10:52:23 +0100
- Subject: Re: [PATCH] Improve ifcombine
- Authentication-results: sourceware.org; auth=none
- References: <20140311155001 dot GD22862 at tucnak dot redhat dot com> <alpine dot LSU dot 2 dot 11 dot 1403120951050 dot 6041 at zhemvz dot fhfr dot qr>
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Wed, Mar 12, 2014 at 09:51:46AM +0100, Richard Biener wrote:
> Ok in principle, but is there a possibility to factor this a bit?
> It looks like a lot of cut&paste (without looking too close for subtle
> differences).
Like this?
2014-03-12 Jakub Jelinek <jakub@redhat.com>
* tree-ssa-ifcombine.c (forwarder_block_to): New function.
(tree_ssa_ifcombine_bb_1): New function.
(tree_ssa_ifcombine_bb): Use it. Handle also cases where else_bb
is an empty forwarder block to then_bb or vice versa and then_bb
and else_bb are effectively swapped.
* gcc.dg/tree-ssa/ssa-ifcombine-12.c: New test.
* gcc.dg/tree-ssa/ssa-ifcombine-13.c: New test.
* gcc.dg/tree-ssa/phi-opt-2.c: Pass -mbranch-cost=1 if
possible, only test for exactly one if if -mbranch-cost=1
has been passed.
--- gcc/tree-ssa-ifcombine.c.jj 2014-03-11 20:14:34.046082392 +0100
+++ gcc/tree-ssa-ifcombine.c 2014-03-12 10:45:29.355054715 +0100
@@ -135,6 +135,16 @@ bb_no_side_effects_p (basic_block bb)
return true;
}
+/* Return true if BB is an empty forwarder block to TO_BB. */
+
+static bool
+forwarder_block_to (basic_block bb, basic_block to_bb)
+{
+ return empty_block_p (bb)
+ && single_succ_p (bb)
+ && single_succ (bb) == to_bb;
+}
+
/* Verify if all PHI node arguments in DEST for edges from BB1 or
BB2 to DEST are the same. This makes the CFG merge point
free from side-effects. Return true in this case, else false. */
@@ -561,6 +571,99 @@ ifcombine_ifandif (basic_block inner_con
return false;
}
+/* Helper function for tree_ssa_ifcombine_bb. Recognize a CFG pattern and
+ dispatch to the appropriate if-conversion helper for a particular
+ set of INNER_COND_BB, OUTER_COND_BB, THEN_BB and ELSE_BB.
+ PHI_PRED_BB should be one of INNER_COND_BB, THEN_BB or ELSE_BB. */
+
+static bool
+tree_ssa_ifcombine_bb_1 (basic_block inner_cond_bb, basic_block outer_cond_bb,
+ basic_block then_bb, basic_block else_bb,
+ basic_block phi_pred_bb)
+{
+ /* The && form is characterized by a common else_bb with
+ the two edges leading to it mergable. The latter is
+ guaranteed by matching PHI arguments in the else_bb and
+ the inner cond_bb having no side-effects. */
+ if (phi_pred_bb != else_bb
+ && recognize_if_then_else (outer_cond_bb, &inner_cond_bb, &else_bb)
+ && same_phi_args_p (outer_cond_bb, phi_pred_bb, else_bb)
+ && bb_no_side_effects_p (inner_cond_bb))
+ {
+ /* We have
+ <outer_cond_bb>
+ if (q) goto inner_cond_bb; else goto else_bb;
+ <inner_cond_bb>
+ if (p) goto ...; else goto else_bb;
+ ...
+ <else_bb>
+ ...
+ */
+ return ifcombine_ifandif (inner_cond_bb, false, outer_cond_bb, false,
+ false);
+ }
+
+ /* And a version where the outer condition is negated. */
+ if (phi_pred_bb != else_bb
+ && recognize_if_then_else (outer_cond_bb, &else_bb, &inner_cond_bb)
+ && same_phi_args_p (outer_cond_bb, phi_pred_bb, else_bb)
+ && bb_no_side_effects_p (inner_cond_bb))
+ {
+ /* We have
+ <outer_cond_bb>
+ if (q) goto else_bb; else goto inner_cond_bb;
+ <inner_cond_bb>
+ if (p) goto ...; else goto else_bb;
+ ...
+ <else_bb>
+ ...
+ */
+ return ifcombine_ifandif (inner_cond_bb, false, outer_cond_bb, true,
+ false);
+ }
+
+ /* The || form is characterized by a common then_bb with the
+ two edges leading to it mergable. The latter is guaranteed
+ by matching PHI arguments in the then_bb and the inner cond_bb
+ having no side-effects. */
+ if (phi_pred_bb != then_bb
+ && recognize_if_then_else (outer_cond_bb, &then_bb, &inner_cond_bb)
+ && same_phi_args_p (outer_cond_bb, phi_pred_bb, then_bb)
+ && bb_no_side_effects_p (inner_cond_bb))
+ {
+ /* We have
+ <outer_cond_bb>
+ if (q) goto then_bb; else goto inner_cond_bb;
+ <inner_cond_bb>
+ if (q) goto then_bb; else goto ...;
+ <then_bb>
+ ...
+ */
+ return ifcombine_ifandif (inner_cond_bb, true, outer_cond_bb, true,
+ true);
+ }
+
+ /* And a version where the outer condition is negated. */
+ if (phi_pred_bb != then_bb
+ && recognize_if_then_else (outer_cond_bb, &inner_cond_bb, &then_bb)
+ && same_phi_args_p (outer_cond_bb, phi_pred_bb, then_bb)
+ && bb_no_side_effects_p (inner_cond_bb))
+ {
+ /* We have
+ <outer_cond_bb>
+ if (q) goto inner_cond_bb; else goto then_bb;
+ <inner_cond_bb>
+ if (q) goto then_bb; else goto ...;
+ <then_bb>
+ ...
+ */
+ return ifcombine_ifandif (inner_cond_bb, true, outer_cond_bb, false,
+ true);
+ }
+
+ return false;
+}
+
/* Recognize a CFG pattern and dispatch to the appropriate
if-conversion helper. We start with BB as the innermost
worker basic-block. Returns true if a transformation was done. */
@@ -585,80 +688,33 @@ tree_ssa_ifcombine_bb (basic_block inner
{
basic_block outer_cond_bb = single_pred (inner_cond_bb);
- /* The && form is characterized by a common else_bb with
- the two edges leading to it mergable. The latter is
- guaranteed by matching PHI arguments in the else_bb and
- the inner cond_bb having no side-effects. */
- if (recognize_if_then_else (outer_cond_bb, &inner_cond_bb, &else_bb)
- && same_phi_args_p (outer_cond_bb, inner_cond_bb, else_bb)
- && bb_no_side_effects_p (inner_cond_bb))
- {
- /* We have
- <outer_cond_bb>
- if (q) goto inner_cond_bb; else goto else_bb;
- <inner_cond_bb>
- if (p) goto ...; else goto else_bb;
- ...
- <else_bb>
- ...
- */
- return ifcombine_ifandif (inner_cond_bb, false, outer_cond_bb, false,
- false);
- }
-
- /* And a version where the outer condition is negated. */
- if (recognize_if_then_else (outer_cond_bb, &else_bb, &inner_cond_bb)
- && same_phi_args_p (outer_cond_bb, inner_cond_bb, else_bb)
- && bb_no_side_effects_p (inner_cond_bb))
- {
- /* We have
- <outer_cond_bb>
- if (q) goto else_bb; else goto inner_cond_bb;
- <inner_cond_bb>
- if (p) goto ...; else goto else_bb;
- ...
- <else_bb>
- ...
- */
- return ifcombine_ifandif (inner_cond_bb, false, outer_cond_bb, true,
- false);
- }
-
- /* The || form is characterized by a common then_bb with the
- two edges leading to it mergable. The latter is guaranteed
- by matching PHI arguments in the then_bb and the inner cond_bb
- having no side-effects. */
- if (recognize_if_then_else (outer_cond_bb, &then_bb, &inner_cond_bb)
- && same_phi_args_p (outer_cond_bb, inner_cond_bb, then_bb)
- && bb_no_side_effects_p (inner_cond_bb))
- {
- /* We have
- <outer_cond_bb>
- if (q) goto then_bb; else goto inner_cond_bb;
- <inner_cond_bb>
- if (q) goto then_bb; else goto ...;
- <then_bb>
- ...
- */
- return ifcombine_ifandif (inner_cond_bb, true, outer_cond_bb, true,
- true);
- }
-
- /* And a version where the outer condition is negated. */
- if (recognize_if_then_else (outer_cond_bb, &inner_cond_bb, &then_bb)
- && same_phi_args_p (outer_cond_bb, inner_cond_bb, then_bb)
- && bb_no_side_effects_p (inner_cond_bb))
- {
- /* We have
- <outer_cond_bb>
- if (q) goto inner_cond_bb; else goto then_bb;
- <inner_cond_bb>
- if (q) goto then_bb; else goto ...;
- <then_bb>
- ...
- */
- return ifcombine_ifandif (inner_cond_bb, true, outer_cond_bb, false,
- true);
+ if (tree_ssa_ifcombine_bb_1 (inner_cond_bb, outer_cond_bb,
+ then_bb, else_bb, inner_cond_bb))
+ return true;
+
+ if (forwarder_block_to (else_bb, then_bb))
+ {
+ /* Other possibilities for the && form, if else_bb is
+ empty forwarder block to then_bb. Compared to the above simpler
+ forms this can be treated as if then_bb and else_bb were swapped,
+ and the corresponding inner_cond_bb not inverted because of that.
+ For same_phi_args_p we look at equality of arguments between
+ edge from outer_cond_bb and the forwarder block. */
+ if (tree_ssa_ifcombine_bb_1 (inner_cond_bb, outer_cond_bb, else_bb,
+ then_bb, else_bb))
+ return true;
+ }
+ else if (forwarder_block_to (then_bb, else_bb))
+ {
+ /* Other possibilities for the || form, if then_bb is
+ empty forwarder block to else_bb. Compared to the above simpler
+ forms this can be treated as if then_bb and else_bb were swapped,
+ and the corresponding inner_cond_bb not inverted because of that.
+ For same_phi_args_p we look at equality of arguments between
+ edge from outer_cond_bb and the forwarder block. */
+ if (tree_ssa_ifcombine_bb_1 (inner_cond_bb, outer_cond_bb, else_bb,
+ then_bb, then_bb))
+ return true;
}
}
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-12.c.jj 2014-03-12 10:23:33.231679541 +0100
+++ gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-12.c 2014-03-12 10:23:33.231679541 +0100
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-tree-vrp -fdump-tree-optimized" } */
+
+/* Testcase for PR31657. */
+
+int f(int x, int a, int b)
+{
+ int t = 0;
+ int c = 1 << a;
+ if (!(x & 1))
+ t = 0;
+ else
+ if (x & (1 << 2))
+ t = 3;
+ else
+ t = 0;
+ return t;
+}
+/* { dg-final { scan-tree-dump "& 5" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-13.c.jj 2014-03-12 10:23:33.231679541 +0100
+++ gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-13.c 2014-03-12 10:23:33.231679541 +0100
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-tree-optimized" } */
+/* { dg-additional-options "-mbranch-cost=2" { target { i?86-*-* x86_64-*-* mips*-*-* s390*-*-* avr*-*-* } } } */
+
+_Bool f1(_Bool a, _Bool b)
+{
+ if (a)
+ {
+ if (b)
+ return 1;
+ else
+ return 0;
+ }
+ return 0;
+}
+
+
+/* For LOGICAL_OP_NON_SHORT_CIRCUIT, this should be optimized
+ into return a & b;, with no ifs. */
+/* { dg-final { scan-tree-dump-not "if" "optimized" { target { i?86-*-* x86_64-*-* mips*-*-* s390*-*-* avr*-*-* } } } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
--- gcc/testsuite/gcc.dg/tree-ssa/phi-opt-2.c.jj 2014-03-11 20:14:33.812083721 +0100
+++ gcc/testsuite/gcc.dg/tree-ssa/phi-opt-2.c 2014-03-12 10:23:33.231679541 +0100
@@ -1,5 +1,6 @@
/* { dg-do compile } */
/* { dg-options "-O1 -fdump-tree-optimized" } */
+/* { dg-additional-options "-mbranch-cost=1" { target { i?86-*-* x86_64-*-* mips*-*-* s390*-*-* avr*-*-* } } } */
_Bool f1(_Bool a, _Bool b)
{
@@ -17,6 +18,8 @@ _Bool f1(_Bool a, _Bool b)
/* There should be only one if, the outer one; the inner one
should have been changed to straight line code with the
value of b (except that we don't fold ! (b != 0) into b
- which can be fixed in a different patch). */
-/* { dg-final { scan-tree-dump-times "if" 1 "optimized"} } */
+ which can be fixed in a different patch).
+ Test this only when known to be !LOGICAL_OP_NON_SHORT_CIRCUIT,
+ otherwise ifcombine may convert this into return a & b;. */
+/* { dg-final { scan-tree-dump-times "if" 1 "optimized" { target { i?86-*-* x86_64-*-* mips*-*-* s390*-*-* avr*-*-* } } } } */
/* { dg-final { cleanup-tree-dump "optimized" } } */
Jakub