atrosinenko created this revision.
atrosinenko added reviewers: scanon, koviankevin, MaskRay, howard.hinnant.
Herald added subscribers: Sanitizers, dberris.
Herald added a project: Sanitizers.
atrosinenko requested review of this revision.
This patch eliminates some other UB in a slightly more tricky way than D86299:
[compiler-rt][builtins] Factor out some common bit manipulations
<https://reviews.llvm.org/D86299>.
- Introduce a `SIGN_OF(signed_int)` macro (not UB-related, just to give this
trick a descriptive name)
- Make the "negate if sign is -1" trick operate on corresponding **unsigned**
types. Not factoring it out due to the "interface" of that macro would probably
be quite error-prone.
This patch is expected to be NFC except for eliminating some UB identified by
unit tests.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D86414
Files:
compiler-rt/lib/builtins/absvdi2.c
compiler-rt/lib/builtins/absvsi2.c
compiler-rt/lib/builtins/absvti2.c
compiler-rt/lib/builtins/floattidf.c
compiler-rt/lib/builtins/floattixf.c
compiler-rt/lib/builtins/int_div_impl.inc
compiler-rt/lib/builtins/int_types.h
Index: compiler-rt/lib/builtins/int_types.h
===================================================================
--- compiler-rt/lib/builtins/int_types.h
+++ compiler-rt/lib/builtins/int_types.h
@@ -60,6 +60,7 @@
#define MIN_SIGNED(type) ((AS_SIGNED(type))SIGN_BIT(type))
#define MAX_SIGNED(type) ((AS_SIGNED(type))(SIGN_BIT(type) - 1U))
#define MAX_UNSIGNED(type) (~(AS_UNSIGNED(type))0))
+#define SIGN_OF(signed_int) ((signed_int) >> (bitsizeof(signed_int) - 1))
typedef union {
di_int all;
Index: compiler-rt/lib/builtins/int_div_impl.inc
===================================================================
--- compiler-rt/lib/builtins/int_div_impl.inc
+++ compiler-rt/lib/builtins/int_div_impl.inc
@@ -71,25 +71,31 @@
#ifdef COMPUTE_UDIV
static __inline fixint_t __divXi3(fixint_t a, fixint_t b) {
- const int N = (int)(sizeof(fixint_t) * CHAR_BIT) - 1;
- fixint_t s_a = a >> N; // s_a = a < 0 ? -1 : 0
- fixint_t s_b = b >> N; // s_b = b < 0 ? -1 : 0
- a = (a ^ s_a) - s_a; // negate if s_a == -1
- b = (b ^ s_b) - s_b; // negate if s_b == -1
- s_a ^= s_b; // sign of quotient
- return (COMPUTE_UDIV(a, b) ^ s_a) - s_a; // negate if s_a == -1
+ // extract signs (0 or -1) of arguments
+ fixint_t s_a = SIGN_OF(a);
+ fixint_t s_b = SIGN_OF(b);
+ // compute absolute values of arguments
+ a = (fixuint_t)(a ^ s_a) - (fixuint_t)s_a;
+ b = (fixuint_t)(b ^ s_b) - (fixuint_t)s_b;
+ // compute a sign of quotient
+ s_a ^= s_b;
+ // compute an absolute value of quotient and negate it if needed
+ return (fixuint_t)(COMPUTE_UDIV(a, b) ^ s_a) - (fixuint_t)s_a;
}
#endif // COMPUTE_UDIV
#ifdef ASSIGN_UMOD
static __inline fixint_t __modXi3(fixint_t a, fixint_t b) {
- const int N = (int)(sizeof(fixint_t) * CHAR_BIT) - 1;
- fixint_t s = b >> N; // s = b < 0 ? -1 : 0
- b = (b ^ s) - s; // negate if s == -1
- s = a >> N; // s = a < 0 ? -1 : 0
- a = (a ^ s) - s; // negate if s == -1
+ // compute an absolute value of b
+ fixint_t s = SIGN_OF(b);
+ b = (fixuint_t)(b ^ s) - (fixuint_t)s;
+ // compute an absolute value of a
+ s = SIGN_OF(a);
+ a = (fixuint_t)(a ^ s) - (fixuint_t)s;
+ // compute an absolute value of the result
fixuint_t res;
ASSIGN_UMOD(res, a, b);
- return (res ^ s) - s; // negate if s == -1
+ // make the result have the same sign as b
+ return (fixuint_t)(res ^ s) - (fixuint_t)s;
}
#endif // ASSIGN_UMOD
Index: compiler-rt/lib/builtins/floattixf.c
===================================================================
--- compiler-rt/lib/builtins/floattixf.c
+++ compiler-rt/lib/builtins/floattixf.c
@@ -26,9 +26,9 @@
COMPILER_RT_ABI long double __floattixf(ti_int a) {
if (a == 0)
return 0.0;
- const unsigned N = sizeof(ti_int) * CHAR_BIT;
- const ti_int s = a >> (N - 1);
- a = (a ^ s) - s;
+ const unsigned N = bitsizeof(ti_int);
+ const ti_int s = SIGN_OF(a);
+ a = (tu_int)(a ^ s) - (tu_int)s;
int sd = N - __clzti2(a); // number of significant digits
int e = sd - 1; // exponent
if (sd > LDBL_MANT_DIG) {
Index: compiler-rt/lib/builtins/floattidf.c
===================================================================
--- compiler-rt/lib/builtins/floattidf.c
+++ compiler-rt/lib/builtins/floattidf.c
@@ -25,9 +25,9 @@
COMPILER_RT_ABI double __floattidf(ti_int a) {
if (a == 0)
return 0.0;
- const unsigned N = sizeof(ti_int) * CHAR_BIT;
- const ti_int s = a >> (N - 1);
- a = (a ^ s) - s;
+ const unsigned N = bitsizeof(ti_int);
+ const ti_int s = SIGN_OF(a);
+ a = (tu_int)(a ^ s) - (tu_int)s;
int sd = N - __clzti2(a); // number of significant digits
int e = sd - 1; // exponent
if (sd > DBL_MANT_DIG) {
Index: compiler-rt/lib/builtins/absvti2.c
===================================================================
--- compiler-rt/lib/builtins/absvti2.c
+++ compiler-rt/lib/builtins/absvti2.c
@@ -19,11 +19,10 @@
// Effects: aborts if abs(x) < 0
COMPILER_RT_ABI ti_int __absvti2(ti_int a) {
- const int N = (int)(sizeof(ti_int) * CHAR_BIT);
- if (a == ((ti_int)1 << (N - 1)))
+ if (a == MIN_SIGNED(ti_int))
compilerrt_abort();
- const ti_int s = a >> (N - 1);
- return (a ^ s) - s;
+ const ti_int t = SIGN_OF(a);
+ return (tu_int)(a ^ t) - (tu_int)t;
}
#endif // CRT_HAS_128BIT
Index: compiler-rt/lib/builtins/absvsi2.c
===================================================================
--- compiler-rt/lib/builtins/absvsi2.c
+++ compiler-rt/lib/builtins/absvsi2.c
@@ -17,9 +17,8 @@
// Effects: aborts if abs(x) < 0
COMPILER_RT_ABI si_int __absvsi2(si_int a) {
- const int N = (int)(sizeof(si_int) * CHAR_BIT);
- if (a == ((si_int)1 << (N - 1)))
+ if (a == MIN_SIGNED(si_int))
compilerrt_abort();
- const si_int t = a >> (N - 1);
- return (a ^ t) - t;
+ const si_int t = SIGN_OF(a);
+ return (su_int)(a ^ t) - (su_int)t;
}
Index: compiler-rt/lib/builtins/absvdi2.c
===================================================================
--- compiler-rt/lib/builtins/absvdi2.c
+++ compiler-rt/lib/builtins/absvdi2.c
@@ -17,9 +17,8 @@
// Effects: aborts if abs(x) < 0
COMPILER_RT_ABI di_int __absvdi2(di_int a) {
- const int N = (int)(sizeof(di_int) * CHAR_BIT);
- if (a == ((di_int)1 << (N - 1)))
+ if (a == MIN_SIGNED(di_int))
compilerrt_abort();
- const di_int t = a >> (N - 1);
- return (a ^ t) - t;
+ const di_int t = SIGN_OF(a);
+ return (du_int)(a ^ t) - (du_int)t;
}
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