* [PATCH 1/2] simplify '(x op x)' to '0', '1' or 'x'
2016-12-07 16:32 [PATCH 0/2] simplify binops with identical operands Luc Van Oostenryck
@ 2016-12-07 16:32 ` Luc Van Oostenryck
2016-12-07 16:32 ` [PATCH 2/2] add warning option '-Wtautological-compare' Luc Van Oostenryck
1 sibling, 0 replies; 3+ messages in thread
From: Luc Van Oostenryck @ 2016-12-07 16:32 UTC (permalink / raw)
To: linux-sparse; +Cc: Christopher Li, Luc Van Oostenryck
Most binops can be simplified when their two operands are
identical. For example '(x ^ x)' can be simplified into '0'.
The cases '(x / x)' and '(x % x)' are not simplified since this
is correct only when x is not zero.
The cases '(x || x)' and '(x && x)' are not simplified because
it's only correct when the operands are booleans/have already
been compared against zero and the linearization don't enforce that.
This patch add the code for these simplifications as well as
their corresponding test cases.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
simplify.c | 35 ++++++++++++++++++++++++++
validation/optim/binops-same-args.c | 49 +++++++++++++++++++++++++++++++++++++
2 files changed, 84 insertions(+)
create mode 100644 validation/optim/binops-same-args.c
diff --git a/simplify.c b/simplify.c
index b5cd0ea7..fde72f0a 100644
--- a/simplify.c
+++ b/simplify.c
@@ -488,6 +488,39 @@ static int simplify_constant_binop(struct instruction *insn)
return REPEAT_CSE;
}
+static int simplify_binop_same_args(struct instruction *insn, pseudo_t arg)
+{
+ switch (insn->opcode) {
+ case OP_SET_NE:
+ case OP_SET_LT: case OP_SET_GT:
+ case OP_SET_B: case OP_SET_A:
+ case OP_SUB:
+ case OP_XOR:
+ return replace_with_pseudo(insn, value_pseudo(0));
+
+ case OP_SET_EQ:
+ case OP_SET_LE: case OP_SET_GE:
+ case OP_SET_BE: case OP_SET_AE:
+ return replace_with_pseudo(insn, value_pseudo(1));
+
+ case OP_AND:
+ case OP_OR:
+ return replace_with_pseudo(insn, arg);
+
+ case OP_AND_BOOL:
+ case OP_OR_BOOL:
+ // simplification is correct only if the operands
+ // have already been compared against zero which
+ // is not enforced.
+ break;
+
+ default:
+ break;
+ }
+
+ return 0;
+}
+
static int simplify_binop(struct instruction *insn)
{
if (dead_insn(insn, &insn->src1, &insn->src2, NULL))
@@ -499,6 +532,8 @@ static int simplify_binop(struct instruction *insn)
}
if (constant(insn->src2))
return simplify_constant_rightside(insn);
+ if (insn->src1 == insn->src2)
+ return simplify_binop_same_args(insn, insn->src1);
return 0;
}
diff --git a/validation/optim/binops-same-args.c b/validation/optim/binops-same-args.c
new file mode 100644
index 00000000..9285655d
--- /dev/null
+++ b/validation/optim/binops-same-args.c
@@ -0,0 +1,49 @@
+typedef unsigned int u32;
+
+int ssub(int a) { return a - a; }
+u32 usub(u32 a) { return a - a; }
+
+int sdiv(int a) { return a / a; }
+u32 udiv(u32 a) { return a / a; }
+int smod(int a) { return a % a; }
+u32 umod(u32 a) { return a % a; }
+
+int seq(int a) { return a == a; }
+int sne(int a) { return a != a; }
+int slt(int a) { return a < a; }
+int sgt(int a) { return a > a; }
+int sle(int a) { return a <= a; }
+int sge(int a) { return a >= a; }
+
+u32 ueq(u32 a) { return a == a; }
+u32 une(u32 a) { return a != a; }
+u32 ult(u32 a) { return a < a; }
+u32 ugt(u32 a) { return a > a; }
+u32 ule(u32 a) { return a <= a; }
+u32 uge(u32 a) { return a >= a; }
+
+u32 xor(u32 a) { return a ^ a; }
+
+u32 ior(u32 a) { return a | a; }
+u32 and(u32 a) { return a & a; }
+
+/*
+ * check-name: double-unop
+ * check-command: test-linearize -Wno-decl $file
+ * check-output-ignore
+ *
+ * check-output-excludes: sub\\.
+ * check-output-contains: divs\\.
+ * check-output-contains: divu\\.
+ * check-output-contains: mods\\.
+ * check-output-contains: modu\\.
+ * check-output-excludes: seteq\\.
+ * check-output-excludes: setne\\.
+ * check-output-excludes: set[gl]t\\.
+ * check-output-excludes: set[gl]e\\.
+ * check-output-excludes: set[ab]\\.
+ * check-output-excludes: set[ab]e\\.
+ * check-output-excludes: xor\\.
+ * check-output-excludes: or\\.
+ * check-output-excludes: and\\.
+ */
--
2.10.2
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH 2/2] add warning option '-Wtautological-compare'
2016-12-07 16:32 [PATCH 0/2] simplify binops with identical operands Luc Van Oostenryck
2016-12-07 16:32 ` [PATCH 1/2] simplify '(x op x)' to '0', '1' or 'x' Luc Van Oostenryck
@ 2016-12-07 16:32 ` Luc Van Oostenryck
1 sibling, 0 replies; 3+ messages in thread
From: Luc Van Oostenryck @ 2016-12-07 16:32 UTC (permalink / raw)
To: linux-sparse; +Cc: Christopher Li, Luc Van Oostenryck
Now that we optimize away expressions like 'x == x' or 'x < x',
also add a warning for it (but disabled by default).
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
lib.c | 2 ++
lib.h | 1 +
simplify.c | 4 ++++
validation/tautological-compare.c | 35 +++++++++++++++++++++++++++++++++++
4 files changed, 42 insertions(+)
create mode 100644 validation/tautological-compare.c
diff --git a/lib.c b/lib.c
index e5b0bb63..6b7a0817 100644
--- a/lib.c
+++ b/lib.c
@@ -236,6 +236,7 @@ int Wptr_subtraction_blows = 0;
int Wreturn_void = 0;
int Wshadow = 0;
int Wsizeof_bool = 0;
+int Wtautological_compare = 0;
int Wtransparent_union = 0;
int Wtypesign = 0;
int Wundef = 0;
@@ -471,6 +472,7 @@ static const struct warning {
{ "return-void", &Wreturn_void },
{ "shadow", &Wshadow },
{ "sizeof-bool", &Wsizeof_bool },
+ { "tautological-compare", &Wtautological_compare },
{ "transparent-union", &Wtransparent_union },
{ "typesign", &Wtypesign },
{ "undef", &Wundef },
diff --git a/lib.h b/lib.h
index 15b69fa2..130e5b6c 100644
--- a/lib.h
+++ b/lib.h
@@ -122,6 +122,7 @@ extern int Wptr_subtraction_blows;
extern int Wreturn_void;
extern int Wshadow;
extern int Wsizeof_bool;
+extern int Wtautological_compare;
extern int Wtransparent_union;
extern int Wtypesign;
extern int Wundef;
diff --git a/simplify.c b/simplify.c
index fde72f0a..b29b3ebb 100644
--- a/simplify.c
+++ b/simplify.c
@@ -494,6 +494,8 @@ static int simplify_binop_same_args(struct instruction *insn, pseudo_t arg)
case OP_SET_NE:
case OP_SET_LT: case OP_SET_GT:
case OP_SET_B: case OP_SET_A:
+ if (Wtautological_compare)
+ warning(insn->pos, "self-comparison always evaluates to false");
case OP_SUB:
case OP_XOR:
return replace_with_pseudo(insn, value_pseudo(0));
@@ -501,6 +503,8 @@ static int simplify_binop_same_args(struct instruction *insn, pseudo_t arg)
case OP_SET_EQ:
case OP_SET_LE: case OP_SET_GE:
case OP_SET_BE: case OP_SET_AE:
+ if (Wtautological_compare)
+ warning(insn->pos, "self-comparison always evaluates to true");
return replace_with_pseudo(insn, value_pseudo(1));
case OP_AND:
diff --git a/validation/tautological-compare.c b/validation/tautological-compare.c
new file mode 100644
index 00000000..55a2b463
--- /dev/null
+++ b/validation/tautological-compare.c
@@ -0,0 +1,35 @@
+typedef unsigned int u32;
+
+int seq(int a) { return a == a; }
+int sne(int a) { return a != a; }
+int slt(int a) { return a < a; }
+int sgt(int a) { return a > a; }
+int sle(int a) { return a <= a; }
+int sge(int a) { return a >= a; }
+
+u32 ueq(u32 a) { return a == a; }
+u32 une(u32 a) { return a != a; }
+u32 ult(u32 a) { return a < a; }
+u32 ugt(u32 a) { return a > a; }
+u32 ule(u32 a) { return a <= a; }
+u32 uge(u32 a) { return a >= a; }
+
+/*
+ * check-name: tautological-compare
+ * check-command: sparse -Wno-decl -Wtautological-compare $file
+ *
+ * check-error-start
+tautological-compare.c:3:30: warning: self-comparison always evaluates to true
+tautological-compare.c:4:30: warning: self-comparison always evaluates to false
+tautological-compare.c:5:29: warning: self-comparison always evaluates to false
+tautological-compare.c:6:29: warning: self-comparison always evaluates to false
+tautological-compare.c:7:30: warning: self-comparison always evaluates to true
+tautological-compare.c:8:30: warning: self-comparison always evaluates to true
+tautological-compare.c:10:30: warning: self-comparison always evaluates to true
+tautological-compare.c:11:30: warning: self-comparison always evaluates to false
+tautological-compare.c:12:29: warning: self-comparison always evaluates to false
+tautological-compare.c:13:29: warning: self-comparison always evaluates to false
+tautological-compare.c:14:30: warning: self-comparison always evaluates to true
+tautological-compare.c:15:30: warning: self-comparison always evaluates to true
+ * check-error-end
+ */
--
2.10.2
^ permalink raw reply related [flat|nested] 3+ messages in thread