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[PATCH] fix c/39902 for decimal float constant folding
- From: Janis Johnson <janis187 at us dot ibm dot com>
- To: gcc-patches at gcc dot gnu dot org
- Date: Fri, 26 Jun 2009 10:33:38 -0700
- Subject: [PATCH] fix c/39902 for decimal float constant folding
- Reply-to: janis187 at us dot ibm dot com
In decimal floating-point arithmetic, trailing zeroes are significant;
the values 1.DD, 1.0DD, and 1.00DD are all different, and arithmetic on
each of those values gives a different result. This means that GCC
should not perform optimizations like replacing (x * 1) with x when
the constant is a decimal float value.
This patch modifies several functions that check for specific values of
real constants so they don't handle decimal float values.
Tested with bootstrap and regtest of all languages but Ada on
powerpc64-linux for -m32/-m64. OK for trunk and, after testing there,
on 4.4 and 4.3 branches? This is not a regression but it does fix
wrong code.
2009-06-26 Janis Johnson <janis187@us.ibm.com>
gcc/
PR c/39902
* tree.c (real_zerop, real_onep, real_twop, real_minus_onep):
Special-case decimal float constants.
gcc/testsuite/
PR c/39902
* gcc.dg/dfp/pr39902.c: New test.
Index: gcc/tree.c
===================================================================
--- gcc/tree.c (revision 148858)
+++ gcc/tree.c (working copy)
@@ -1591,7 +1591,8 @@ tree_floor_log2 (const_tree expr)
: floor_log2 (low));
}
-/* Return 1 if EXPR is the real constant zero. */
+/* Return 1 if EXPR is the real constant zero. Trailing zeroes matter for
+ decimal float constants, so don't return 1 for them. */
int
real_zerop (const_tree expr)
@@ -1599,13 +1600,16 @@ real_zerop (const_tree expr)
STRIP_NOPS (expr);
return ((TREE_CODE (expr) == REAL_CST
- && REAL_VALUES_EQUAL (TREE_REAL_CST (expr), dconst0))
+ && REAL_VALUES_EQUAL (TREE_REAL_CST (expr), dconst0)
+ && !(DECIMAL_FLOAT_MODE_P (TYPE_MODE (TREE_TYPE (expr)))))
|| (TREE_CODE (expr) == COMPLEX_CST
&& real_zerop (TREE_REALPART (expr))
&& real_zerop (TREE_IMAGPART (expr))));
}
-/* Return 1 if EXPR is the real constant one in real or complex form. */
+/* Return 1 if EXPR is the real constant one in real or complex form.
+ Trailing zeroes matter for decimal float constants, so don't return
+ 1 for them. */
int
real_onep (const_tree expr)
@@ -1613,13 +1617,15 @@ real_onep (const_tree expr)
STRIP_NOPS (expr);
return ((TREE_CODE (expr) == REAL_CST
- && REAL_VALUES_EQUAL (TREE_REAL_CST (expr), dconst1))
+ && REAL_VALUES_EQUAL (TREE_REAL_CST (expr), dconst1)
+ && !(DECIMAL_FLOAT_MODE_P (TYPE_MODE (TREE_TYPE (expr)))))
|| (TREE_CODE (expr) == COMPLEX_CST
&& real_onep (TREE_REALPART (expr))
&& real_zerop (TREE_IMAGPART (expr))));
}
-/* Return 1 if EXPR is the real constant two. */
+/* Return 1 if EXPR is the real constant two. Trailing zeroes matter
+ for decimal float constants, so don't return 1 for them. */
int
real_twop (const_tree expr)
@@ -1627,13 +1633,15 @@ real_twop (const_tree expr)
STRIP_NOPS (expr);
return ((TREE_CODE (expr) == REAL_CST
- && REAL_VALUES_EQUAL (TREE_REAL_CST (expr), dconst2))
+ && REAL_VALUES_EQUAL (TREE_REAL_CST (expr), dconst2)
+ && !(DECIMAL_FLOAT_MODE_P (TYPE_MODE (TREE_TYPE (expr)))))
|| (TREE_CODE (expr) == COMPLEX_CST
&& real_twop (TREE_REALPART (expr))
&& real_zerop (TREE_IMAGPART (expr))));
}
-/* Return 1 if EXPR is the real constant minus one. */
+/* Return 1 if EXPR is the real constant minus one. Trailing zeroes
+ matter for decimal float constants, so don't return 1 for them. */
int
real_minus_onep (const_tree expr)
@@ -1641,7 +1649,8 @@ real_minus_onep (const_tree expr)
STRIP_NOPS (expr);
return ((TREE_CODE (expr) == REAL_CST
- && REAL_VALUES_EQUAL (TREE_REAL_CST (expr), dconstm1))
+ && REAL_VALUES_EQUAL (TREE_REAL_CST (expr), dconstm1)
+ && !(DECIMAL_FLOAT_MODE_P (TYPE_MODE (TREE_TYPE (expr)))))
|| (TREE_CODE (expr) == COMPLEX_CST
&& real_minus_onep (TREE_REALPART (expr))
&& real_zerop (TREE_IMAGPART (expr))));
Index: gcc/testsuite/gcc.dg/dfp/pr39902.c
===================================================================
--- gcc/testsuite/gcc.dg/dfp/pr39902.c (revision 0)
+++ gcc/testsuite/gcc.dg/dfp/pr39902.c (revision 0)
@@ -0,0 +1,239 @@
+/* { dg-options "--std=gnu99" } */
+
+/* Check that optimizations like (x * 1) to x, or (x * -1) to -x,
+ do not apply to decimal float computations where trailing zeroes
+ are significant. */
+
+extern void abort (void);
+int failcnt;
+
+#ifdef DBG
+extern int printf (const char *, ...);
+#define FAILURE { printf ("failed at line %d\n", __LINE__); failcnt++; }
+#else
+#define FAILURE abort ();
+#endif
+
+#define COMPARE32(A,B) \
+ A.i == B.i
+
+#define COMPARE64(A,B) \
+ A.i[0] == B.i[0] && A.i[1] == B.i[1]
+
+#define COMPARE128(A,B) \
+ A.i[0] == B.i[0] && A.i[1] == B.i[1] && A.i[2] == B.i[2] && A.i[3] == B.i[3]
+
+typedef union {
+ _Decimal32 d;
+ unsigned int i;
+} u32;
+
+typedef union {
+ _Decimal64 d;
+ unsigned int i[2];
+} u64;
+
+typedef union {
+ _Decimal128 d;
+ unsigned int i[4];
+} u128;
+
+volatile u32 p32_1;
+volatile u32 p32_1_0;
+volatile u32 p32_2_0;
+volatile u32 m32_1;
+volatile u32 m32_1_0;
+volatile u32 m32_2_0;
+volatile u32 a32;
+
+volatile u64 p64_1;
+volatile u64 p64_1_0;
+volatile u64 p64_2_0;
+volatile u64 m64_1;
+volatile u64 m64_1_0;
+volatile u64 m64_2_0;
+volatile u64 a64;
+
+volatile u128 p128_1;
+volatile u128 p128_1_0;
+volatile u128 p128_2_0;
+volatile u128 m128_1;
+volatile u128 m128_1_0;
+volatile u128 m128_2_0;
+volatile u128 a128;
+
+void
+init32 (void)
+{
+ p32_1.d = 1.DF;
+ p32_1_0.d = 1.0DF;
+ p32_2_0.d = 2.0DF;
+ m32_1.d = -1.DF;
+ m32_1_0.d = -1.0DF;
+ m32_2_0.d = -2.0DF;
+}
+
+void
+init64 (void)
+{
+ p64_1.d = 1.DD;
+ p64_1_0.d = 1.0DD;
+ p64_2_0.d = 2.0DD;
+ m64_1.d = -1.DD;
+ m64_1_0.d = -1.0DD;
+ m64_2_0.d = -2.0DD;
+}
+
+void
+init128 (void)
+{
+ p128_1.d = 1.DL;
+ p128_1_0.d = 1.0DL;
+ p128_2_0.d = 2.0DL;
+ m128_1.d = -1.DL;
+ m128_1_0.d = -1.0DL;
+ m128_2_0.d = -2.0DL;
+}
+
+void
+doit32 (void)
+{
+ /* Multiplying by a value with no trailing zero should not change the
+ quantum exponent. */
+
+ a32.d = p32_2_0.d * p32_1.d;
+ if (! (COMPARE32 (a32, p32_2_0)))
+ FAILURE
+
+ a32.d = p32_2_0.d * 1.DF;
+ if (! (COMPARE32 (a32, p32_2_0)))
+ FAILURE
+
+ a32.d = p32_2_0.d * m32_1.d;
+ if (! (COMPARE32 (a32, m32_2_0)))
+ FAILURE
+
+ a32.d = p32_2_0.d * -1.DF;
+ if (! (COMPARE32 (a32, m32_2_0)))
+ FAILURE
+
+ /* Multiplying by a value with a trailing zero should change the
+ quantum exponent. */
+
+ a32.d = p32_2_0.d * p32_1_0.d;
+ if (COMPARE32 (a32, p32_2_0))
+ FAILURE
+
+ a32.d = p32_2_0.d * 1.0DF;
+ if (COMPARE32 (a32, p32_2_0))
+ FAILURE
+
+ a32.d = p32_2_0.d * m32_1_0.d;
+ if (COMPARE32 (a32, m32_2_0))
+ FAILURE
+
+ a32.d = p32_2_0.d * -1.0DF;
+ if (COMPARE32 (a32, m32_2_0))
+ FAILURE
+}
+
+void
+doit64 (void)
+{
+ /* Multiplying by a value with no trailing zero should not change the
+ quantum exponent. */
+
+ a64.d = p64_2_0.d * p64_1.d;
+ if (! (COMPARE64 (a64, p64_2_0)))
+ FAILURE
+
+ a64.d = p64_2_0.d * 1.DD;
+ if (! (COMPARE64 (a64, p64_2_0)))
+ FAILURE
+
+ a64.d = p64_2_0.d * m64_1.d;
+ if (! (COMPARE64 (a64, m64_2_0)))
+ FAILURE
+
+ a64.d = p64_2_0.d * -1.DD;
+ if (! (COMPARE64 (a64, m64_2_0)))
+ FAILURE
+
+ /* Multiplying by a value with a trailing zero should change the
+ quantum exponent. */
+
+ a64.d = p64_2_0.d * p64_1_0.d;
+ if (COMPARE64 (a64, p64_2_0))
+ FAILURE
+
+ a64.d = p64_2_0.d * 1.0DD;
+ if (COMPARE64 (a64, p64_2_0))
+ FAILURE
+
+ a64.d = p64_2_0.d * m64_1_0.d;
+ if (COMPARE64 (a64, m64_2_0))
+ FAILURE
+
+ a64.d = p64_2_0.d * -1.0DD;
+ if (COMPARE64 (a64, m64_2_0))
+ FAILURE
+}
+
+void
+doit128 (void)
+{
+ /* Multiplying by a value with no trailing zero should not change the
+ quantum exponent. */
+
+ a128.d = p128_2_0.d * p128_1_0.d;
+ if (COMPARE128 (a128, p128_2_0))
+ FAILURE
+
+ a128.d = p128_2_0.d * 1.0DD;
+ if (COMPARE128 (a128, p128_2_0))
+ FAILURE
+
+ a128.d = p128_2_0.d * m128_1_0.d;
+ if (COMPARE128 (a128, m128_2_0))
+ FAILURE
+
+ a128.d = p128_2_0.d * -1.0DD;
+ if (COMPARE128 (a128, m128_2_0))
+ FAILURE
+
+ /* Multiplying by a value with a trailing zero should change the
+ quantum exponent. */
+
+ a128.d = p128_2_0.d * p128_1.d;
+ if (! (COMPARE128 (a128, p128_2_0)))
+ FAILURE
+
+ a128.d = p128_2_0.d * 1.DD;
+ if (! (COMPARE128 (a128, p128_2_0)))
+ FAILURE
+
+ a128.d = p128_2_0.d * m128_1.d;
+ if (! (COMPARE128 (a128, m128_2_0)))
+ FAILURE
+
+ a128.d = p128_2_0.d * -1.DD;
+ if (! (COMPARE128 (a128, m128_2_0)))
+ FAILURE
+}
+
+int
+main (void)
+{
+ init32 ();
+ init64 ();
+ init128 ();
+
+ doit32 ();
+ doit64 ();
+ doit128 ();
+
+ if (failcnt != 0)
+ abort ();
+
+ return 0;
+}