Currently, we warn if the right operand of a shift expression is negative,
or greater than or equal to the length in bits of the promoted left operand.
But we don't warn when we see a left shift of a negative value. That is
undefined behavior since C99 and I believe C++11, so this patch implements
a new warning, -Wshift-negative-value, only active in C99/C++11.
A bunch of tests needed tweaking; I find it scary that some vect tests are
invoking UB.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2015-04-22 Marek Polacek <pola...@redhat.com>
PR c/65179
* c-common.c (c_fully_fold_internal): Warn when left shifting a
negative value.
* c.opt (Wshift-negative-value): New option.
* c-typeck.c (build_binary_op): Warn when left shifting a negative
value.
* typeck.c (cp_build_binary_op): Warn when left shifting a negative
value.
* doc/invoke.texi: Document -Wshift-negative-value.
* c-c++-common/Wshift-negative-value-1.c: New test.
* c-c++-common/Wshift-negative-value-2.c: New test.
* c-c++-common/torture/vector-shift2.c: Use -Wno-shift-negative-value.
* gcc.dg/torture/vector-shift2.c: Likewise.
* gcc.c-torture/execute/pr40386.c: Likewise.
* gcc.dg/tree-ssa/vrp65.c: Likewise.
* gcc.dg/tree-ssa/vrp66.c: Likewise.
* gcc.dg/vect/vect-sdivmod-1.c: Likewise.
* gcc.dg/vect/vect-shift-2-big-array.c: Likewise.
* gcc.dg/vect/vect-shift-2.c: Likewise.
* gcc.target/i386/pr31167.c: Likewise.
* g++.dg/init/array11.C: Add dg-warning.
* gcc.dg/c99-const-expr-7.c: Add dg-warning and dg-error.
diff --git gcc/c-family/c-common.c gcc/c-family/c-common.c
index 7fe7fa6..e944f11 100644
--- gcc/c-family/c-common.c
+++ gcc/c-family/c-common.c
@@ -1361,6 +1361,15 @@ c_fully_fold_internal (tree expr, bool in_init, bool
*maybe_const_operands,
&& !TREE_OVERFLOW_P (op0)
&& !TREE_OVERFLOW_P (op1))
overflow_warning (EXPR_LOCATION (expr), ret);
+ if (code == LSHIFT_EXPR
+ && TREE_CODE (orig_op0) != INTEGER_CST
+ && TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
+ && TREE_CODE (op0) == INTEGER_CST
+ && c_inhibit_evaluation_warnings == 0
+ && tree_int_cst_sgn (op0) < 0
+ && flag_isoc99)
+ warning_at (loc, OPT_Wshift_negative_value,
+ "left shift of negative value");
if ((code == LSHIFT_EXPR || code == RSHIFT_EXPR)
&& TREE_CODE (orig_op1) != INTEGER_CST
&& TREE_CODE (op1) == INTEGER_CST
diff --git gcc/c-family/c.opt gcc/c-family/c.opt
index 983f4a8..47e0913 100644
--- gcc/c-family/c.opt
+++ gcc/c-family/c.opt
@@ -781,6 +781,10 @@ Wshift-count-overflow
C ObjC C++ ObjC++ Var(warn_shift_count_overflow) Init(1) Warning
Warn if shift count >= width of type
+Wshift-negative-value
+C ObjC C++ ObjC++ Var(warn_shift_negative_value) Init(1) Warning
+Warn if left shifting a negative value
+
Wsign-compare
C ObjC C++ ObjC++ Var(warn_sign_compare) Warning LangEnabledBy(C++ ObjC++,Wall)
Warn about signed-unsigned comparisons
diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index ebe4c73..17d2cac 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -10701,6 +10701,15 @@ build_binary_op (location_t location, enum tree_code
code,
&& code1 == INTEGER_TYPE)
{
doing_shift = true;
+ if (TREE_CODE (op0) == INTEGER_CST
+ && tree_int_cst_sgn (op0) < 0
+ && flag_isoc99)
+ {
+ int_const = false;
+ if (c_inhibit_evaluation_warnings == 0)
+ warning_at (location, OPT_Wshift_negative_value,
+ "left shift of negative value");
+ }
if (TREE_CODE (op1) == INTEGER_CST)
{
if (tree_int_cst_sgn (op1) < 0)
diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index 250b5d6..d5d36bf 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -4327,11 +4327,21 @@ cp_build_binary_op (location_t location,
}
else if (code0 == INTEGER_TYPE && code1 == INTEGER_TYPE)
{
+ tree const_op0 = fold_non_dependent_expr (op0);
+ if (TREE_CODE (const_op0) != INTEGER_CST)
+ const_op0 = op0;
tree const_op1 = fold_non_dependent_expr (op1);
if (TREE_CODE (const_op1) != INTEGER_CST)
const_op1 = op1;
result_type = type0;
doing_shift = true;
+ if (TREE_CODE (const_op0) == INTEGER_CST
+ && tree_int_cst_sgn (const_op0) < 0
+ && (complain & tf_warning)
+ && c_inhibit_evaluation_warnings == 0
+ && cxx_dialect >= cxx11)
+ warning (OPT_Wshift_negative_value,
+ "left shift of negative value");
if (TREE_CODE (const_op1) == INTEGER_CST)
{
if (tree_int_cst_lt (const_op1, integer_zero_node))
diff --git gcc/doc/invoke.texi gcc/doc/invoke.texi
index a939ff7..2e14921 100644
--- gcc/doc/invoke.texi
+++ gcc/doc/invoke.texi
@@ -271,7 +271,7 @@ Objective-C and Objective-C++ Dialects}.
-Wpointer-arith -Wno-pointer-to-int-cast @gol
-Wredundant-decls -Wno-return-local-addr @gol
-Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar @gol
--Wshift-count-negative -Wshift-count-overflow @gol
+-Wshift-count-negative -Wshift-count-overflow -Wshift-negative-value @gol
-Wsign-compare -Wsign-conversion -Wfloat-conversion @gol
-Wsizeof-pointer-memaccess -Wsizeof-array-argument @gol
-Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol
@@ -3914,6 +3914,12 @@ Warn if shift count is negative. This warning is enabled
by default.
@opindex Wno-shift-count-overflow
Warn if shift count >= width of type. This warning is enabled by default.
+@item -Wshift-negative-value
+@opindex Wshift-negative-value
+@opindex Wno-shift-negative-value
+Warn if left shifting a negative value. This warning only occurs in C99 and
+C++11 modes (and newer). This warning is enabled by default.
+
@item -Wswitch
@opindex Wswitch
@opindex Wno-switch
diff --git gcc/testsuite/c-c++-common/Wshift-negative-value-1.c
gcc/testsuite/c-c++-common/Wshift-negative-value-1.c
index e69de29..49104e8 100644
--- gcc/testsuite/c-c++-common/Wshift-negative-value-1.c
+++ gcc/testsuite/c-c++-common/Wshift-negative-value-1.c
@@ -0,0 +1,49 @@
+/* PR c/65179 */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+/* { dg-additional-options "-std=c++11" { target c++ } } */
+
+enum E {
+ A = 0 << 1,
+ B = 1 << 1,
+ C = -1 << 1, /* { dg-warning "left shift of negative value" } */
+ D = 0 >> 1,
+ E = 1 >> 1,
+ F = -1 >> 1
+};
+
+int
+left (int x)
+{
+ /* Warn for LSHIFT_EXPR. */
+ const int z = 0;
+ const int o = 1;
+ const int m = -1;
+ int r = 0;
+ r += z << x;
+ r += o << x;
+ r += m << x; /* { dg-warning "left shift of negative value" } */
+ r += 0 << x;
+ r += 1 << x;
+ r += -1 << x; /* { dg-warning "left shift of negative value" } */
+ r += -1U << x;
+ return r;
+}
+
+int
+right (int x)
+{
+ /* Shouldn't warn for RSHIFT_EXPR. */
+ const int z = 0;
+ const int o = 1;
+ const int m = -1;
+ int r = 0;
+ r += z >> x;
+ r += o >> x;
+ r += m >> x;
+ r += 0 >> x;
+ r += 1 >> x;
+ r += -1 >> x;
+ r += -1U >> x;
+ return r;
+}
diff --git gcc/testsuite/c-c++-common/Wshift-negative-value-2.c
gcc/testsuite/c-c++-common/Wshift-negative-value-2.c
index e69de29..0aea931 100644
--- gcc/testsuite/c-c++-common/Wshift-negative-value-2.c
+++ gcc/testsuite/c-c++-common/Wshift-negative-value-2.c
@@ -0,0 +1,49 @@
+/* PR c/65179 */
+/* { dg-do compile } */
+/* { dg-options "-O -Wno-shift-negative-value" } */
+/* { dg-additional-options "-std=c++11" { target c++ } } */
+
+enum E {
+ A = 0 << 1,
+ B = 1 << 1,
+ C = -1 << 1, /* { dg-bogus "left shift of negative value" } */
+ D = 0 >> 1,
+ E = 1 >> 1,
+ F = -1 >> 1
+};
+
+int
+left (int x)
+{
+ /* Warn for LSHIFT_EXPR. */
+ const int z = 0;
+ const int o = 1;
+ const int m = -1;
+ int r = 0;
+ r += z << x;
+ r += o << x;
+ r += m << x; /* { dg-bogus "left shift of negative value" } */
+ r += 0 << x;
+ r += 1 << x;
+ r += -1 << x; /* { dg-bogus "left shift of negative value" } */
+ r += -1U << x;
+ return r;
+}
+
+int
+right (int x)
+{
+ /* Shouldn't warn for RSHIFT_EXPR. */
+ const int z = 0;
+ const int o = 1;
+ const int m = -1;
+ int r = 0;
+ r += z >> x;
+ r += o >> x;
+ r += m >> x;
+ r += 0 >> x;
+ r += 1 >> x;
+ r += -1 >> x;
+ r += -1U >> x;
+ return r;
+}
diff --git gcc/testsuite/c-c++-common/torture/vector-shift2.c
gcc/testsuite/c-c++-common/torture/vector-shift2.c
index d3a2ef8..6d280d8 100644
--- gcc/testsuite/c-c++-common/torture/vector-shift2.c
+++ gcc/testsuite/c-c++-common/torture/vector-shift2.c
@@ -1,4 +1,6 @@
/* { dg-do run } */
+/* { dg-additional-options "-Wno-shift-negative-value" } */
+
#define vector(elcount, type) \
__attribute__((vector_size((elcount)*sizeof(type)))) type
diff --git gcc/testsuite/g++.dg/init/array11.C
gcc/testsuite/g++.dg/init/array11.C
index e52effe..096b145 100644
--- gcc/testsuite/g++.dg/init/array11.C
+++ gcc/testsuite/g++.dg/init/array11.C
@@ -21,7 +21,7 @@ struct gdt gdt_table[2]=
{
{
0,
- ( (((size_t)(&x))<<(24))&(-1<<(8)) ),
+ ( (((size_t)(&x))<<(24))&(-1<<(8)) ), // { dg-warning "left
shift of negative value" "" { target c++11 } }
},
};
}
diff --git gcc/testsuite/gcc.c-torture/execute/pr40386.c
gcc/testsuite/gcc.c-torture/execute/pr40386.c
index f39f1de..15966f6 100644
--- gcc/testsuite/gcc.c-torture/execute/pr40386.c
+++ gcc/testsuite/gcc.c-torture/execute/pr40386.c
@@ -1,4 +1,4 @@
-/* { dg-options "-fno-ira-share-spill-slots" } */
+/* { dg-options "-fno-ira-share-spill-slots -Wno-shift-negative-value" } */
extern void abort (void);
extern void exit (int);
diff --git gcc/testsuite/gcc.dg/c99-const-expr-7.c
gcc/testsuite/gcc.dg/c99-const-expr-7.c
index b872077..ef87722 100644
--- gcc/testsuite/gcc.dg/c99-const-expr-7.c
+++ gcc/testsuite/gcc.dg/c99-const-expr-7.c
@@ -30,8 +30,8 @@ int f1 = (0 ? 0 << -1 : 0);
int g1 = (0 ? 0 >> 1000 : 0);
int h1 = (0 ? 0 >> -1: 0);
-/* Allowed for now, but actually undefined behavior in C99. */
-int i = -1 << 0;
+int i = -1 << 0; /* { dg-warning "left shift of negative value" } */
+/* { dg-error "constant" "constant" { target *-*-* } 33 } */
int j[1] = { DBL_MAX }; /* { dg-warning "overflow in implicit constant
conversion" } */
/* { dg-error "overflow in constant expression" "constant" { target *-*-* } 36
} */
diff --git gcc/testsuite/gcc.dg/torture/vector-shift2.c
gcc/testsuite/gcc.dg/torture/vector-shift2.c
index 0e8a0eb..2cb3bdc 100644
--- gcc/testsuite/gcc.dg/torture/vector-shift2.c
+++ gcc/testsuite/gcc.dg/torture/vector-shift2.c
@@ -1,4 +1,5 @@
/* { dg-do run } */
+/* { dg-additional-options "-Wno-shift-negative-value" } */
#define vector(elcount, type) \
__attribute__((vector_size((elcount)*sizeof(type)))) type
diff --git gcc/testsuite/gcc.dg/tree-ssa/vrp65.c
gcc/testsuite/gcc.dg/tree-ssa/vrp65.c
index d109068..a118c71 100644
--- gcc/testsuite/gcc.dg/tree-ssa/vrp65.c
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp65.c
@@ -1,6 +1,6 @@
/* PR tree-optimization/52267 */
/* { dg-do link } */
-/* { dg-options "-O2" } */
+/* { dg-options "-O2 -Wno-shift-negative-value" } */
extern void link_error (void);
diff --git gcc/testsuite/gcc.dg/tree-ssa/vrp66.c
gcc/testsuite/gcc.dg/tree-ssa/vrp66.c
index 6a6ab34..76cbeed 100644
--- gcc/testsuite/gcc.dg/tree-ssa/vrp66.c
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp66.c
@@ -1,6 +1,6 @@
/* PR tree-optimization/52267 */
/* { dg-do run { target { ! int16 } } } */
-/* { dg-options "-O2" } */
+/* { dg-options "-O2 -Wno-shift-negative-value" } */
extern void abort (void);
diff --git gcc/testsuite/gcc.dg/vect/vect-sdivmod-1.c
gcc/testsuite/gcc.dg/vect/vect-sdivmod-1.c
index c18204e..2f5e86d 100644
--- gcc/testsuite/gcc.dg/vect/vect-sdivmod-1.c
+++ gcc/testsuite/gcc.dg/vect/vect-sdivmod-1.c
@@ -1,3 +1,5 @@
+/* { dg-additional-options "-Wno-shift-negative-value" } */
+
#include "tree-vect.h"
extern void abort (void);
diff --git gcc/testsuite/gcc.dg/vect/vect-shift-2-big-array.c
gcc/testsuite/gcc.dg/vect/vect-shift-2-big-array.c
index 0e1acfb..a36dc5e 100644
--- gcc/testsuite/gcc.dg/vect/vect-shift-2-big-array.c
+++ gcc/testsuite/gcc.dg/vect/vect-shift-2-big-array.c
@@ -1,3 +1,4 @@
+/* { dg-additional-options "-Wno-shift-negative-value" } */
/* { dg-require-effective-target vect_shift } */
/* { dg-require-effective-target vect_int } */
/* Check the standard integer types for left and right shifts to see if the
diff --git gcc/testsuite/gcc.dg/vect/vect-shift-2.c
gcc/testsuite/gcc.dg/vect/vect-shift-2.c
index 83211eb..4388b78 100644
--- gcc/testsuite/gcc.dg/vect/vect-shift-2.c
+++ gcc/testsuite/gcc.dg/vect/vect-shift-2.c
@@ -1,3 +1,4 @@
+/* { dg-additional-options "-Wno-shift-negative-value" } */
/* { dg-require-effective-target vect_shift } */
/* { dg-require-effective-target vect_int } */
/* Check the standard integer types for left and right shifts to see if the
diff --git gcc/testsuite/gcc.target/i386/pr31167.c
gcc/testsuite/gcc.target/i386/pr31167.c
index 43d9f84..5470d36 100644
--- gcc/testsuite/gcc.target/i386/pr31167.c
+++ gcc/testsuite/gcc.target/i386/pr31167.c
@@ -1,6 +1,6 @@
/* { dg-do compile } */
/* { dg-require-effective-target int128 } */
-/* { dg-options "-O" } */
+/* { dg-options "-O -Wno-shift-negative-value" } */
typedef int int32_t;
Marek
