The linearization step sometimes creates a lot of intermediate
basic blocks, often containing just a branch. Their presence often
make things more complicated than needed (more work to do in later
phases, visual clutter when inspection the IR 'by hand') and they
can sometimes, indirectly hinder some optimizations.
Happily, most of them can trivially be optimized away.
So, add a CFG simplification phase running very early and doing:
*) jump threading (eliminate jump to jump)
*) merge single-child/sinle-parents basic blocks.
These changes slightly decrease the number of 'context imbalance'
warnings (32 less on a total of 995 warnings) and the size of
the generated IR (only ~0.4% but this is very significant relatively
to most other simplifications).
They also seem to improve the kernel tests' running time:
before after
real 4m19.261s real 4m17.548s
user 72m03.634s user 71m34.642s
sys 29m05.573s sys 29m01.856s
but it's probably just noise.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
flow.c | 78 ++++++++++++++++++++
flow.h | 1 +
optimize.c | 5 ++
validation/call-inlined.c | 4 +
validation/expand/builtin_constant_inline0.c | 1 +
validation/inline_base0.c | 3 +
validation/linear/builtin_unreachable0.c | 4 +-
validation/linear/builtin_unreachable1.c | 4 +-
validation/linear/call-inline.c | 2 +-
validation/mem2reg/cond-expr.c | 4 +-
validation/mem2reg/cond-expr5.c | 5 +-
validation/optim/cse-size.c | 2 +-
12 files changed, 102 insertions(+), 11 deletions(-)
diff --git a/flow.c b/flow.c
index 23886f9d84fa..f56e72db470c 100644
--- a/flow.c
+++ b/flow.c
@@ -121,6 +121,31 @@ static int bb_depends_on_phi(struct basic_block *target, struct basic_block *src
return 0;
}
+///
+// does the BB contains ignorable instructions but a final branch?
+// :note: something could be done for phi-sources but ... we'll see.
+static bool bb_is_forwarder(struct basic_block *bb)
+{
+ struct instruction *insn;
+
+ FOR_EACH_PTR(bb->insns, insn) {
+ if (!insn->bb)
+ continue;
+ switch (insn->opcode) {
+ case OP_NOP:
+ case OP_INLINED_CALL:
+ continue;
+ case OP_CBR:
+ case OP_BR:
+ return true;
+ default:
+ goto out;
+ }
+ } END_FOR_EACH_PTR(insn);
+out:
+ return false;
+}
+
/*
* When we reach here, we have:
* - a basic block that ends in a conditional branch and
@@ -742,6 +767,22 @@ void vrfy_flow(struct entrypoint *ep)
assert(!entry);
}
+static int retarget_parents(struct basic_block *bb, struct basic_block *target)
+{
+ struct basic_block *parent;
+
+ /*
+ * We can't do FOR_EACH_PTR() here, because the parent list
+ * may change when we rewrite the parent.
+ */
+ while ((parent = first_basic_block(bb->parents))) {
+ if (!rewrite_parent_branch(parent, bb, target))
+ return 0;
+ }
+ kill_bb(bb);
+ return REPEAT_CFG_CLEANUP;
+}
+
static void adjust_phisrc(struct basic_block *top, struct instruction *insn)
{
struct instruction *user = get_phinode(insn);
@@ -821,6 +862,43 @@ static int merge_bb(struct basic_block *top, struct basic_block *bot)
return REPEAT_CFG_CLEANUP;
}
+///
+// early simplification of the CFG
+// Three things are done here:
+// # inactive BB are removed
+// # branches to a 'forwarder' BB are redirected to the forwardee.
+// # merge single-child/single-parent BBs.
+int simplify_cfg_early(struct entrypoint *ep)
+{
+ struct basic_block *bb;
+ int changed = 0;
+
+ FOR_EACH_PTR_REVERSE(ep->bbs, bb) {
+ struct instruction *insn;
+ struct basic_block *tgt;
+
+ if (!bb->ep) {
+ DELETE_CURRENT_PTR(bb);
+ changed = REPEAT_CFG_CLEANUP;
+ continue;
+ }
+
+ insn = last_instruction(bb->insns);
+ if (!insn)
+ continue;
+ switch (insn->opcode) {
+ case OP_BR:
+ tgt = insn->bb_true;
+ if (bb_is_forwarder(bb))
+ changed |= retarget_parents(bb, tgt);
+ else if (bb_list_size(tgt->parents) == 1)
+ changed |= merge_bb(bb, tgt);
+ break;
+ }
+ } END_FOR_EACH_PTR_REVERSE(bb);
+ return changed;
+}
+
void pack_basic_blocks(struct entrypoint *ep)
{
struct basic_block *bb;
diff --git a/flow.h b/flow.h
index 099767d408f5..19a743c83b94 100644
--- a/flow.h
+++ b/flow.h
@@ -18,6 +18,7 @@ extern void kill_dead_stores(struct entrypoint *ep, pseudo_t addr, int local);
extern void simplify_symbol_usage(struct entrypoint *ep);
extern void simplify_memops(struct entrypoint *ep);
extern void pack_basic_blocks(struct entrypoint *ep);
+extern int simplify_cfg_early(struct entrypoint *ep);
extern void convert_instruction_target(struct instruction *insn, pseudo_t src);
extern void remove_dead_insns(struct entrypoint *);
diff --git a/optimize.c b/optimize.c
index 8ab105bccdce..338714c78e68 100644
--- a/optimize.c
+++ b/optimize.c
@@ -57,6 +57,11 @@ void optimize(struct entrypoint *ep)
kill_unreachable_bbs(ep);
ir_validate(ep);
+ cfg_postorder(ep);
+ if (simplify_cfg_early(ep))
+ kill_unreachable_bbs(ep);
+ ir_validate(ep);
+
domtree_build(ep);
/*
diff --git a/validation/call-inlined.c b/validation/call-inlined.c
index 3612c5c42690..a6cb4b5b0976 100644
--- a/validation/call-inlined.c
+++ b/validation/call-inlined.c
@@ -28,12 +28,14 @@ foo:
<entry-point>
add.32 %r3 <- %arg1, %arg2
add.32 %r5 <- %r3, $1
+ # call %r6 <- add, %r3, $1
ret.32 %r5
bar:
.L3:
<entry-point>
+ # call %r13 <- add, %r10, $1
ret
@@ -41,6 +43,7 @@ bas:
.L6:
<entry-point>
add.64 %r16 <- "abc", $1
+ # call %r17 <- lstrip, %r14
ret.64 %r16
@@ -48,6 +51,7 @@ qus:
.L9:
<entry-point>
add.64 %r21 <- messg, $1
+ # call %r22 <- lstrip, %r19
ret.64 %r21
diff --git a/validation/expand/builtin_constant_inline0.c b/validation/expand/builtin_constant_inline0.c
index a0057f2094b3..d72a211fd267 100644
--- a/validation/expand/builtin_constant_inline0.c
+++ b/validation/expand/builtin_constant_inline0.c
@@ -16,6 +16,7 @@ int foo(void)
foo:
.L0:
<entry-point>
+ # call %r1 <- is_const, $42
ret.32 $42
diff --git a/validation/inline_base0.c b/validation/inline_base0.c
index 517ee972ee05..698c760ff0be 100644
--- a/validation/inline_base0.c
+++ b/validation/inline_base0.c
@@ -27,6 +27,7 @@ foo0:
.L0:
<entry-point>
add.32 %r5 <- %arg1, %arg2
+ # call %r6 <- add, %r1, %r2
ret.32 %r5
@@ -34,12 +35,14 @@ foo1:
.L3:
<entry-point>
add.32 %r10 <- %arg1, $1
+ # call %r11 <- add, %r8, $1
ret.32 %r10
foo2:
.L6:
<entry-point>
+ # call %r13 <- add, $1, $2
ret.32 $3
diff --git a/validation/linear/builtin_unreachable0.c b/validation/linear/builtin_unreachable0.c
index 911ed7f97f95..4fc564739e76 100644
--- a/validation/linear/builtin_unreachable0.c
+++ b/validation/linear/builtin_unreachable0.c
@@ -14,12 +14,12 @@ foo:
.L0:
<entry-point>
seteq.32 %r2 <- %arg1, $3
- cbr %r2, .L1, .L3
+ cbr %r2, .L1, .L2
.L1:
unreachable
-.L3:
+.L2:
ret.32 %arg1
diff --git a/validation/linear/builtin_unreachable1.c b/validation/linear/builtin_unreachable1.c
index 70f6674c6443..2fc1d728d7d9 100644
--- a/validation/linear/builtin_unreachable1.c
+++ b/validation/linear/builtin_unreachable1.c
@@ -16,9 +16,9 @@ int foo(int c)
foo:
.L0:
<entry-point>
- cbr %arg1, .L3, .L2
+ cbr %arg1, .L1, .L2
-.L3:
+.L1:
ret.32 $1
.L2:
diff --git a/validation/linear/call-inline.c b/validation/linear/call-inline.c
index dfd49b62c4b7..1ad785ee678b 100644
--- a/validation/linear/call-inline.c
+++ b/validation/linear/call-inline.c
@@ -13,6 +13,6 @@ int i3(void) { return (***fun)(); } // C99,C11 6.5.3.2p4
*
* check-output-ignore
* check-output-excludes: load
- * check-output-excludes: call
+ * check-output-excludes: \\tcall
* check-output-pattern(5): ret\\..* \\$42
*/
diff --git a/validation/mem2reg/cond-expr.c b/validation/mem2reg/cond-expr.c
index 8acb00ac950f..2474d65d8c64 100644
--- a/validation/mem2reg/cond-expr.c
+++ b/validation/mem2reg/cond-expr.c
@@ -9,6 +9,6 @@ int foo(int a, int b, int c)
* check-name: cond-expr
* check-command: test-linearize -Wno-decl -fdump-ir=mem2reg $file
* check-output-ignore
- * check-output-pattern(2): phi\\.
- * check-output-pattern(3): phisrc\\.
+ * check-output-pattern(1): phi\\.
+ * check-output-pattern(2): phisrc\\.
*/
diff --git a/validation/mem2reg/cond-expr5.c b/validation/mem2reg/cond-expr5.c
index a3ce5e3a955e..beef8f258cd9 100644
--- a/validation/mem2reg/cond-expr5.c
+++ b/validation/mem2reg/cond-expr5.c
@@ -15,7 +15,6 @@ int foo(int p, int q, int a)
* check-output-ignore
* check-output-excludes: load\\.
* check-output-excludes: store\\.
- * check-output-excludes: phi\\..*, .*, .*
- * check-output-pattern(3): phi\\.
- * check-output-pattern(5): phisrc\\.
+ * check-output-pattern(2): phi\\.
+ * check-output-pattern(4): phisrc\\.
*/
diff --git a/validation/optim/cse-size.c b/validation/optim/cse-size.c
index e1a5d492a666..0c0c2d1425ed 100644
--- a/validation/optim/cse-size.c
+++ b/validation/optim/cse-size.c
@@ -13,6 +13,6 @@ static void foo(void)
* check-command: test-linearize -Wno-decl $file
*
* check-output-ignore
- * check-output-pattern(0,1): phi\\.
+ * check-output-excludes: phi\\.
* check-output-excludes: cbr
*/
--
2.29.2
