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When compiling compiler-rt with -fsanitize=undefined and running testcases you end up with the following warning: UBSan:/repo/uabkaka/llvm-project/compiler-rt/lib/builtins/int_mulo_impl.inc:24:23: signed integer overflow: -1 * -2147483648 cannot be represented in type 'si_int' (aka 'long') This can be avoided by doing the multiplication in a matching unsigned variant of the type. This was found in an out of tree target. Reviewed By: phosek Differential Revision: https://reviews.llvm.org/D146623
50 lines
1.4 KiB
C
50 lines
1.4 KiB
C
//===-- int_mulo_impl.inc - Implement __mulo[sdt]i4 ---------------*- C -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Helper used by __mulosi4, __mulodi4 and __muloti4.
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//
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//===----------------------------------------------------------------------===//
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#include "int_lib.h"
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// Returns: a * b
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// Effects: sets *overflow to 1 if a * b overflows
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static __inline fixint_t __muloXi4(fixint_t a, fixint_t b, int *overflow) {
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const int N = (int)(sizeof(fixint_t) * CHAR_BIT);
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const fixint_t MIN = (fixint_t)((fixuint_t)1 << (N - 1));
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const fixint_t MAX = ~MIN;
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*overflow = 0;
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fixint_t result = (fixuint_t)a * b;
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if (a == MIN) {
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if (b != 0 && b != 1)
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*overflow = 1;
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return result;
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}
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if (b == MIN) {
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if (a != 0 && a != 1)
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*overflow = 1;
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return result;
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}
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fixint_t sa = a >> (N - 1);
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fixint_t abs_a = (a ^ sa) - sa;
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fixint_t sb = b >> (N - 1);
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fixint_t abs_b = (b ^ sb) - sb;
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if (abs_a < 2 || abs_b < 2)
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return result;
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if (sa == sb) {
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if (abs_a > MAX / abs_b)
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*overflow = 1;
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} else {
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if (abs_a > MIN / -abs_b)
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*overflow = 1;
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}
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return result;
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}
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