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[builtins] Fix ABI-incompatibility with GCC for floating-point compare 

While implementing support for the float128 routines on x86_64, I noticed
that __builtin_isinf() was returning true for 128-bit floating point
values that are not infinite when compiling with GCC and using the
compiler-rt implementation of the soft-float comparison functions.
After stepping through the assembly, I discovered that this was caused by
GCC assuming a sign-extended 64-bit -1 result, but our implementation
returns an enum (which then has zeroes in the upper bits) and therefore
causes the comparison with -1 to fail.

Fix this by using a CMP_RESULT typedef and add a static_assert that it
matches the GCC soft-float comparison return type when compiling with GCC
(GCC has a __libgcc_cmp_return__ mode that can be used for this purpose).

Also move the 3 copies of the same code to a shared .inc file.

Reviewed By: compnerd

Differential Revision: https://reviews.llvm.org/D98205
This commit is contained in:
Alex Richardson 2021-04-21 12:20:06 +01:00
parent 9692811b26
commit 777ca513c8
4 changed files with 131 additions and 234 deletions
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84
compiler-rt/lib/builtins/comparedf2.c
View File

@ -39,47 +39,9 @@
#define DOUBLE_PRECISION
#include "fp_lib.h"
enum LE_RESULT { LE_LESS = -1, LE_EQUAL = 0, LE_GREATER = 1, LE_UNORDERED = 1 };
#include "fp_compare_impl.inc"
COMPILER_RT_ABI enum LE_RESULT __ledf2(fp_t a, fp_t b) {
const srep_t aInt = toRep(a);
const srep_t bInt = toRep(b);
const rep_t aAbs = aInt & absMask;
const rep_t bAbs = bInt & absMask;
// If either a or b is NaN, they are unordered.
if (aAbs > infRep || bAbs > infRep)
return LE_UNORDERED;
// If a and b are both zeros, they are equal.
if ((aAbs | bAbs) == 0)
return LE_EQUAL;
// If at least one of a and b is positive, we get the same result comparing
// a and b as signed integers as we would with a floating-point compare.
if ((aInt & bInt) >= 0) {
if (aInt < bInt)
return LE_LESS;
else if (aInt == bInt)
return LE_EQUAL;
else
return LE_GREATER;
}
// Otherwise, both are negative, so we need to flip the sense of the
// comparison to get the correct result. (This assumes a twos- or ones-
// complement integer representation; if integers are represented in a
// sign-magnitude representation, then this flip is incorrect).
else {
if (aInt > bInt)
return LE_LESS;
else if (aInt == bInt)
return LE_EQUAL;
else
return LE_GREATER;
}
}
COMPILER_RT_ABI CMP_RESULT __ledf2(fp_t a, fp_t b) { return __leXf2__(a, b); }
#if defined(__ELF__)
// Alias for libgcc compatibility
@ -89,48 +51,12 @@ COMPILER_RT_ALIAS(__ledf2, __eqdf2)
COMPILER_RT_ALIAS(__ledf2, __ltdf2)
COMPILER_RT_ALIAS(__ledf2, __nedf2)
enum GE_RESULT {
GE_LESS = -1,
GE_EQUAL = 0,
GE_GREATER = 1,
GE_UNORDERED = -1 // Note: different from LE_UNORDERED
};
COMPILER_RT_ABI enum GE_RESULT __gedf2(fp_t a, fp_t b) {
const srep_t aInt = toRep(a);
const srep_t bInt = toRep(b);
const rep_t aAbs = aInt & absMask;
const rep_t bAbs = bInt & absMask;
if (aAbs > infRep || bAbs > infRep)
return GE_UNORDERED;
if ((aAbs | bAbs) == 0)
return GE_EQUAL;
if ((aInt & bInt) >= 0) {
if (aInt < bInt)
return GE_LESS;
else if (aInt == bInt)
return GE_EQUAL;
else
return GE_GREATER;
} else {
if (aInt > bInt)
return GE_LESS;
else if (aInt == bInt)
return GE_EQUAL;
else
return GE_GREATER;
}
}
COMPILER_RT_ABI CMP_RESULT __gedf2(fp_t a, fp_t b) { return __geXf2__(a, b); }
COMPILER_RT_ALIAS(__gedf2, __gtdf2)
COMPILER_RT_ABI int
__unorddf2(fp_t a, fp_t b) {
const rep_t aAbs = toRep(a) & absMask;
const rep_t bAbs = toRep(b) & absMask;
return aAbs > infRep || bAbs > infRep;
COMPILER_RT_ABI CMP_RESULT __unorddf2(fp_t a, fp_t b) {
return __unordXf2__(a, b);
}
#if defined(__ARM_EABI__)

84
compiler-rt/lib/builtins/comparesf2.c
View File

@ -39,47 +39,9 @@
#define SINGLE_PRECISION
#include "fp_lib.h"
enum LE_RESULT { LE_LESS = -1, LE_EQUAL = 0, LE_GREATER = 1, LE_UNORDERED = 1 };
#include "fp_compare_impl.inc"
COMPILER_RT_ABI enum LE_RESULT __lesf2(fp_t a, fp_t b) {
const srep_t aInt = toRep(a);
const srep_t bInt = toRep(b);
const rep_t aAbs = aInt & absMask;
const rep_t bAbs = bInt & absMask;
// If either a or b is NaN, they are unordered.
if (aAbs > infRep || bAbs > infRep)
return LE_UNORDERED;
// If a and b are both zeros, they are equal.
if ((aAbs | bAbs) == 0)
return LE_EQUAL;
// If at least one of a and b is positive, we get the same result comparing
// a and b as signed integers as we would with a fp_ting-point compare.
if ((aInt & bInt) >= 0) {
if (aInt < bInt)
return LE_LESS;
else if (aInt == bInt)
return LE_EQUAL;
else
return LE_GREATER;
}
// Otherwise, both are negative, so we need to flip the sense of the
// comparison to get the correct result. (This assumes a twos- or ones-
// complement integer representation; if integers are represented in a
// sign-magnitude representation, then this flip is incorrect).
else {
if (aInt > bInt)
return LE_LESS;
else if (aInt == bInt)
return LE_EQUAL;
else
return LE_GREATER;
}
}
COMPILER_RT_ABI CMP_RESULT __lesf2(fp_t a, fp_t b) { return __leXf2__(a, b); }
#if defined(__ELF__)
// Alias for libgcc compatibility
@ -89,48 +51,12 @@ COMPILER_RT_ALIAS(__lesf2, __eqsf2)
COMPILER_RT_ALIAS(__lesf2, __ltsf2)
COMPILER_RT_ALIAS(__lesf2, __nesf2)
enum GE_RESULT {
GE_LESS = -1,
GE_EQUAL = 0,
GE_GREATER = 1,
GE_UNORDERED = -1 // Note: different from LE_UNORDERED
};
COMPILER_RT_ABI enum GE_RESULT __gesf2(fp_t a, fp_t b) {
const srep_t aInt = toRep(a);
const srep_t bInt = toRep(b);
const rep_t aAbs = aInt & absMask;
const rep_t bAbs = bInt & absMask;
if (aAbs > infRep || bAbs > infRep)
return GE_UNORDERED;
if ((aAbs | bAbs) == 0)
return GE_EQUAL;
if ((aInt & bInt) >= 0) {
if (aInt < bInt)
return GE_LESS;
else if (aInt == bInt)
return GE_EQUAL;
else
return GE_GREATER;
} else {
if (aInt > bInt)
return GE_LESS;
else if (aInt == bInt)
return GE_EQUAL;
else
return GE_GREATER;
}
}
COMPILER_RT_ABI CMP_RESULT __gesf2(fp_t a, fp_t b) { return __geXf2__(a, b); }
COMPILER_RT_ALIAS(__gesf2, __gtsf2)
COMPILER_RT_ABI int
__unordsf2(fp_t a, fp_t b) {
const rep_t aAbs = toRep(a) & absMask;
const rep_t bAbs = toRep(b) & absMask;
return aAbs > infRep || bAbs > infRep;
COMPILER_RT_ABI CMP_RESULT __unordsf2(fp_t a, fp_t b) {
return __unordXf2__(a, b);
}
#if defined(__ARM_EABI__)

81
compiler-rt/lib/builtins/comparetf2.c
View File

@ -40,45 +40,9 @@
#include "fp_lib.h"
#if defined(CRT_HAS_128BIT) && defined(CRT_LDBL_128BIT)
enum LE_RESULT { LE_LESS = -1, LE_EQUAL = 0, LE_GREATER = 1, LE_UNORDERED = 1 };
#include "fp_compare_impl.inc"
COMPILER_RT_ABI enum LE_RESULT __letf2(fp_t a, fp_t b) {
const srep_t aInt = toRep(a);
const srep_t bInt = toRep(b);
const rep_t aAbs = aInt & absMask;
const rep_t bAbs = bInt & absMask;
// If either a or b is NaN, they are unordered.
if (aAbs > infRep || bAbs > infRep)
return LE_UNORDERED;
// If a and b are both zeros, they are equal.
if ((aAbs | bAbs) == 0)
return LE_EQUAL;
// If at least one of a and b is positive, we get the same result comparing
// a and b as signed integers as we would with a floating-point compare.
if ((aInt & bInt) >= 0) {
if (aInt < bInt)
return LE_LESS;
else if (aInt == bInt)
return LE_EQUAL;
else
return LE_GREATER;
} else {
// Otherwise, both are negative, so we need to flip the sense of the
// comparison to get the correct result. (This assumes a twos- or ones-
// complement integer representation; if integers are represented in a
// sign-magnitude representation, then this flip is incorrect).
if (aInt > bInt)
return LE_LESS;
else if (aInt == bInt)
return LE_EQUAL;
else
return LE_GREATER;
}
}
COMPILER_RT_ABI CMP_RESULT __letf2(fp_t a, fp_t b) { return __leXf2__(a, b); }
#if defined(__ELF__)
// Alias for libgcc compatibility
@ -88,47 +52,12 @@ COMPILER_RT_ALIAS(__letf2, __eqtf2)
COMPILER_RT_ALIAS(__letf2, __lttf2)
COMPILER_RT_ALIAS(__letf2, __netf2)
enum GE_RESULT {
GE_LESS = -1,
GE_EQUAL = 0,
GE_GREATER = 1,
GE_UNORDERED = -1 // Note: different from LE_UNORDERED
};
COMPILER_RT_ABI enum GE_RESULT __getf2(fp_t a, fp_t b) {
const srep_t aInt = toRep(a);
const srep_t bInt = toRep(b);
const rep_t aAbs = aInt & absMask;
const rep_t bAbs = bInt & absMask;
if (aAbs > infRep || bAbs > infRep)
return GE_UNORDERED;
if ((aAbs | bAbs) == 0)
return GE_EQUAL;
if ((aInt & bInt) >= 0) {
if (aInt < bInt)
return GE_LESS;
else if (aInt == bInt)
return GE_EQUAL;
else
return GE_GREATER;
} else {
if (aInt > bInt)
return GE_LESS;
else if (aInt == bInt)
return GE_EQUAL;
else
return GE_GREATER;
}
}
COMPILER_RT_ABI CMP_RESULT __getf2(fp_t a, fp_t b) { return __geXf2__(a, b); }
COMPILER_RT_ALIAS(__getf2, __gttf2)
COMPILER_RT_ABI int __unordtf2(fp_t a, fp_t b) {
const rep_t aAbs = toRep(a) & absMask;
const rep_t bAbs = toRep(b) & absMask;
return aAbs > infRep || bAbs > infRep;
COMPILER_RT_ABI CMP_RESULT __unordtf2(fp_t a, fp_t b) {
return __unordXf2__(a, b);
}
#endif

116
compiler-rt/lib/builtins/fp_compare_impl.inc Normal file
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@ -0,0 +1,116 @@
//===-- lib/fp_compare_impl.inc - Floating-point comparison -------*- C -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "fp_lib.h"
// GCC uses long (at least for x86_64) as the return type of the comparison
// functions. We need to ensure that the return value is sign-extended in the
// same way as GCC expects (since otherwise GCC-generated __builtin_isinf
// returns true for finite 128-bit floating-point numbers).
#ifdef __aarch64__
// AArch64 GCC overrides libgcc_cmp_return to use int instead of long.
typedef int CMP_RESULT;
#elif __SIZEOF_POINTER__ == 8 && __SIZEOF_LONG__ == 4
// LLP64 ABIs use long long instead of long.
typedef long long CMP_RESULT;
#else
// Otherwise the comparison functions return long.
typedef long CMP_RESULT;
#endif
#if !defined(__clang__) && defined(__GNUC__)
// GCC uses a special __libgcc_cmp_return__ mode to define the return type, so
// check that we are ABI-compatible when compiling the builtins with GCC.
typedef int GCC_CMP_RESULT __attribute__((__mode__(__libgcc_cmp_return__)));
_Static_assert(sizeof(GCC_CMP_RESULT) == sizeof(CMP_RESULT),
"SOFTFP ABI not compatible with GCC");
#endif
enum {
LE_LESS = -1,
LE_EQUAL = 0,
LE_GREATER = 1,
LE_UNORDERED = 1,
};
static inline CMP_RESULT __leXf2__(fp_t a, fp_t b) {
const srep_t aInt = toRep(a);
const srep_t bInt = toRep(b);
const rep_t aAbs = aInt & absMask;
const rep_t bAbs = bInt & absMask;
// If either a or b is NaN, they are unordered.
if (aAbs > infRep || bAbs > infRep)
return LE_UNORDERED;
// If a and b are both zeros, they are equal.
if ((aAbs | bAbs) == 0)
return LE_EQUAL;
// If at least one of a and b is positive, we get the same result comparing
// a and b as signed integers as we would with a floating-point compare.
if ((aInt & bInt) >= 0) {
if (aInt < bInt)
return LE_LESS;
else if (aInt == bInt)
return LE_EQUAL;
else
return LE_GREATER;
} else {
// Otherwise, both are negative, so we need to flip the sense of the
// comparison to get the correct result. (This assumes a twos- or ones-
// complement integer representation; if integers are represented in a
// sign-magnitude representation, then this flip is incorrect).
if (aInt > bInt)
return LE_LESS;
else if (aInt == bInt)
return LE_EQUAL;
else
return LE_GREATER;
}
}
enum {
GE_LESS = -1,
GE_EQUAL = 0,
GE_GREATER = 1,
GE_UNORDERED = -1 // Note: different from LE_UNORDERED
};
static inline CMP_RESULT __geXf2__(fp_t a, fp_t b) {
const srep_t aInt = toRep(a);
const srep_t bInt = toRep(b);
const rep_t aAbs = aInt & absMask;
const rep_t bAbs = bInt & absMask;
if (aAbs > infRep || bAbs > infRep)
return GE_UNORDERED;
if ((aAbs | bAbs) == 0)
return GE_EQUAL;
if ((aInt & bInt) >= 0) {
if (aInt < bInt)
return GE_LESS;
else if (aInt == bInt)
return GE_EQUAL;
else
return GE_GREATER;
} else {
if (aInt > bInt)
return GE_LESS;
else if (aInt == bInt)
return GE_EQUAL;
else
return GE_GREATER;
}
}
static inline CMP_RESULT __unordXf2__(fp_t a, fp_t b) {
const rep_t aAbs = toRep(a) & absMask;
const rep_t bAbs = toRep(b) & absMask;
return aAbs > infRep || bAbs > infRep;
}