From 02de9d26b1820e4af35ebdd271c3a788e3c99035 Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Wed, 24 Aug 2022 14:10:25 +0000 Subject: [PATCH] tree.cc: Fix optimization of DFP default initialization When an object of decimal floating-point type is default-initialized, GCC is inconsistent about whether it is given the all-zero-bits representation (zero with the least quantum exponent) or whether it acts like a conversion of integer 0 to the DFP type (zero with quantum exponent 0). In particular, the representation stored in memory can have all zero bits, but optimization of access to the same object based on its known constant value can then produce zero with quantum exponent 0 instead. C2x leaves the quantum exponent for default initialization implementation-defined, but that doesn't allow such inconsistency in the interpretation of a single object. All zero bits seems most appropriate; change build_real to special-case dconst0 the same way other constants are special-cased and ensure that the correct zero for the type is generated. Bootstrapped with no regressions for x86_64-pc-linux-gnu. gcc/ * tree.cc (build_real): Give DFP dconst0 the minimum quantum exponent for the type. gcc/testsuite/ * gcc.dg/torture/dfp-default-init-1.c, gcc.dg/torture/dfp-default-init-2.c, gcc.dg/torture/dfp-default-init-3.c: New tests. --- gcc/testsuite/gcc.dg/torture/dfp-default-init-1.c | 113 ++++++++++++++++++++++ gcc/testsuite/gcc.dg/torture/dfp-default-init-2.c | 8 ++ gcc/testsuite/gcc.dg/torture/dfp-default-init-3.c | 8 ++ gcc/tree.cc | 13 ++- 4 files changed, 140 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/torture/dfp-default-init-1.c create mode 100644 gcc/testsuite/gcc.dg/torture/dfp-default-init-2.c create mode 100644 gcc/testsuite/gcc.dg/torture/dfp-default-init-3.c diff --git a/gcc/testsuite/gcc.dg/torture/dfp-default-init-1.c b/gcc/testsuite/gcc.dg/torture/dfp-default-init-1.c new file mode 100644 index 0000000..f893ddb --- /dev/null +++ b/gcc/testsuite/gcc.dg/torture/dfp-default-init-1.c @@ -0,0 +1,113 @@ +/* Test that default-initialized DFP values consistently have the least quantum + exponent. */ +/* { dg-do run } */ +/* { dg-require-effective-target dfp } */ + +extern void exit (int); +extern void abort (void); +void *memset (void *, int, __SIZE_TYPE__); +int memcmp (const void *, const void *, __SIZE_TYPE__); + +#ifndef TYPE +#define TYPE _Decimal32 +#endif + +#ifndef ZEROFP +#define ZEROFP 0e-101DF +#endif + +TYPE zero_int = 0; +TYPE zero_fp = ZEROFP; +TYPE default_init; +TYPE zero_bytes; +TYPE x; + +struct s { TYPE a, b; }; +struct s s_default_init; +struct s s_empty_init = {}; +struct s s_first_int = { 0 }; +struct s s_both_int = { 0, 0 }; +struct s sx; + +const TYPE a_default_init[10]; +const TYPE a_empty_init[10] = {}; +const TYPE a_first_int[10] = { 0 }; +const TYPE a_two_int[10] = { 0, 0 }; + +#define CHECK_ZERO_BYTES(expr) \ + do \ + { \ + if (memcmp (expr, &zero_bytes, sizeof zero_bytes) != 0) \ + abort (); \ + TYPE tmp = *expr; \ + if (memcmp (&tmp, &zero_bytes, sizeof zero_bytes) != 0) \ + abort (); \ + } \ + while (0) + +#define CHECK_INT_BYTES(expr) \ + do \ + { \ + if (memcmp (expr, &zero_int, sizeof zero_int) != 0) \ + abort (); \ + TYPE tmp = *expr; \ + if (memcmp (&tmp, &zero_int, sizeof zero_int) != 0) \ + abort (); \ + } \ + while (0) + +int +main (void) +{ + memset (&zero_bytes, 0, sizeof zero_bytes); + if (memcmp (&zero_bytes, &zero_int, sizeof zero_int) == 0) + abort (); + CHECK_ZERO_BYTES (&zero_fp); + CHECK_ZERO_BYTES (&default_init); + CHECK_ZERO_BYTES (&s_default_init.a); + CHECK_ZERO_BYTES (&s_default_init.b); + CHECK_ZERO_BYTES (&s_empty_init.a); + CHECK_ZERO_BYTES (&s_empty_init.b); + CHECK_INT_BYTES (&s_first_int.a); + CHECK_ZERO_BYTES (&s_first_int.b); + CHECK_INT_BYTES (&s_both_int.a); + CHECK_INT_BYTES (&s_both_int.b); + CHECK_ZERO_BYTES (&a_default_init[0]); + CHECK_ZERO_BYTES (&a_default_init[1]); + CHECK_ZERO_BYTES (&a_default_init[2]); + CHECK_ZERO_BYTES (&a_default_init[9]); + CHECK_ZERO_BYTES (&a_empty_init[0]); + CHECK_ZERO_BYTES (&a_empty_init[1]); + CHECK_ZERO_BYTES (&a_empty_init[2]); + CHECK_ZERO_BYTES (&a_empty_init[9]); + CHECK_INT_BYTES (&a_first_int[0]); + CHECK_ZERO_BYTES (&a_first_int[1]); + CHECK_ZERO_BYTES (&a_first_int[2]); + CHECK_ZERO_BYTES (&a_first_int[9]); + CHECK_INT_BYTES (&a_two_int[0]); + CHECK_INT_BYTES (&a_two_int[1]); + CHECK_ZERO_BYTES (&a_two_int[2]); + CHECK_ZERO_BYTES (&a_two_int[9]); + struct s s2 = {}; + CHECK_ZERO_BYTES (&s2.a); + CHECK_ZERO_BYTES (&s2.b); + struct s s3 = { 0 }; + CHECK_INT_BYTES (&s3.a); + CHECK_ZERO_BYTES (&s3.b); + struct s s4 = { 0, 0 }; + CHECK_INT_BYTES (&s4.a); + CHECK_INT_BYTES (&s4.b); + struct s s5 = { 0 }; + sx = s5; + CHECK_INT_BYTES (&sx.a); + CHECK_ZERO_BYTES (&sx.b); + x = default_init; + CHECK_ZERO_BYTES (&x); + x = zero_int; + CHECK_INT_BYTES (&x); + x = s_default_init.a; + CHECK_ZERO_BYTES (&x); + x = s_default_init.b; + CHECK_ZERO_BYTES (&x); + exit (0); +} diff --git a/gcc/testsuite/gcc.dg/torture/dfp-default-init-2.c b/gcc/testsuite/gcc.dg/torture/dfp-default-init-2.c new file mode 100644 index 0000000..30f850b --- /dev/null +++ b/gcc/testsuite/gcc.dg/torture/dfp-default-init-2.c @@ -0,0 +1,8 @@ +/* Test that default-initialized DFP values consistently have the least quantum + exponent. */ +/* { dg-do run } */ +/* { dg-require-effective-target dfp } */ + +#define TYPE _Decimal64 +#define ZEROFP 0e-398DD +#include "dfp-default-init-1.c" diff --git a/gcc/testsuite/gcc.dg/torture/dfp-default-init-3.c b/gcc/testsuite/gcc.dg/torture/dfp-default-init-3.c new file mode 100644 index 0000000..cdf7350 --- /dev/null +++ b/gcc/testsuite/gcc.dg/torture/dfp-default-init-3.c @@ -0,0 +1,8 @@ +/* Test that default-initialized DFP values consistently have the least quantum + exponent. */ +/* { dg-do run } */ +/* { dg-require-effective-target dfp } */ + +#define TYPE _Decimal128 +#define ZEROFP 0e-6176DL +#include "dfp-default-init-1.c" diff --git a/gcc/tree.cc b/gcc/tree.cc index fed1434..007c932 100644 --- a/gcc/tree.cc +++ b/gcc/tree.cc @@ -2385,12 +2385,12 @@ build_real (tree type, REAL_VALUE_TYPE d) tree v; int overflow = 0; - /* dconst{1,2,m1,half} are used in various places in + /* dconst{0,1,2,m1,half} are used in various places in the middle-end and optimizers, allow them here even for decimal floating point types as an exception by converting them to decimal. */ if (DECIMAL_FLOAT_MODE_P (TYPE_MODE (type)) - && d.cl == rvc_normal + && (d.cl == rvc_normal || d.cl == rvc_zero) && !d.decimal) { if (memcmp (&d, &dconst1, sizeof (d)) == 0) @@ -2401,6 +2401,15 @@ build_real (tree type, REAL_VALUE_TYPE d) decimal_real_from_string (&d, "-1"); else if (memcmp (&d, &dconsthalf, sizeof (d)) == 0) decimal_real_from_string (&d, "0.5"); + else if (memcmp (&d, &dconst0, sizeof (d)) == 0) + { + /* Make sure to give zero the minimum quantum exponent for + the type (which corresponds to all bits zero). */ + const struct real_format *fmt = REAL_MODE_FORMAT (TYPE_MODE (type)); + char buf[16]; + sprintf (buf, "0e%d", fmt->emin - fmt->p); + decimal_real_from_string (&d, buf); + } else gcc_unreachable (); } -- 2.7.4