This bug fixes PR 68404, which created an insn for the fusion operation when
accessing an array with a large constant offset that the downstream passes
(regrenam in particular don't like). Because fusion in general adds so little
to the performance of power8, I just eliminated the compiler from generating
this case for GCC 6. In the GCC 7 timeframe, I likely will revist fusion for
power9 support. I ran a spec 2006 benchmark suite comparing the current
behavior and the fix for PR 68404, and it was in the noise level (mcf was 1%
slower, others ranged from 0.3% slower to 0.4% faster).
I did a bootstrap build, including a bootstrap profiled build with LTO (which
is how the problem was found) and it was found. I rewrote 2 of the 3 fusion
tests so that it uses fusion from a medium code toc entry instead of accessing
an array element with a constant index over 65536 bytes.
Is this patch ok to apply? If you would prefer, I can eliminate the code
inside of the fusion_gpr_addis predicate instead of using #if 0.
[gcc]
2016-02-08 Michael Meissner
PR target/68404
* config/rs6000/predicates.md (fusion_gpr_addis): Prevent fusing
an ADDIS that adds a pointer to a large constant that sets the
upper16 bits with a load operation.
[gcc/testsuite]
2016-02-08 Michael Meissner
PR target/68404
* gcc.target/powerpc/fusion.c: Rewrite test to use TOC fusion
instead accessing a really large arrray.
* gcc.target/powerpc/fusion3.c: Likewise.
--
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meiss...@linux.vnet.ibm.com, phone: +1 (978) 899-4797
Index: gcc/config/rs6000/predicates.md
===
--- gcc/config/rs6000/predicates.md (revision 233220)
+++ gcc/config/rs6000/predicates.md (working copy)
@@ -1716,10 +1716,17 @@ (define_predicate "fusion_gpr_addis"
if (CONST_INT_P (op))
int_const = op;
+#if 0
+ /* PR 68404 -- regrename doesn't like:
+
+ (mem (plus (plus (reg)
+(const_int))
+ (const_int */
else if (GET_CODE (op) == PLUS
&& base_reg_operand (XEXP (op, 0), Pmode)
&& CONST_INT_P (XEXP (op, 1)))
int_const = XEXP (op, 1);
+#endif
else
return 0;
Index: gcc/testsuite/gcc.target/powerpc/fusion3.c
===
--- gcc/testsuite/gcc.target/powerpc/fusion3.c (revision 233220)
+++ gcc/testsuite/gcc.target/powerpc/fusion3.c (working copy)
@@ -4,15 +4,24 @@
/* { dg-skip-if "do not override -mcpu" { powerpc*-*-* } { "-mcpu=*" } {
"-mcpu=power7" } } */
/* { dg-options "-mcpu=power7 -mtune=power9 -O3" } */
-#define LARGE 0x12345
+#define SIZE 4
+struct foo {
+ float f;
+ double d;
+};
-int fusion_float_read (float *p){ return p[LARGE]; }
-int fusion_double_read (double *p){ return p[LARGE]; }
+static struct foo st[SIZE];
+struct foo *ptr_st = &st[0];
-void fusion_float_write (float *p, float f){ p[LARGE] = f; }
-void fusion_double_write (double *p, double d){ p[LARGE] = d; }
+float fusion_float_read (void){ return st[SIZE].f; }
+double fusion_float_extend (void){ return (double)st[SIZE].f; }
+double fusion_double_read (void){ return st[SIZE].d; }
-/* { dg-final { scan-assembler "load fusion, type SF" } } */
-/* { dg-final { scan-assembler "load fusion, type DF" } } */
-/* { dg-final { scan-assembler "store fusion, type SF" } } */
-/* { dg-final { scan-assembler "store fusion, type DF" } } */
+void fusion_float_write (float f){ st[SIZE].f = f; }
+void fusion_float_truncate (double d){ st[SIZE].f = (float)d; }
+void fusion_double_write (double d){ st[SIZE].d = d; }
+
+/* { dg-final { scan-assembler-times "load fusion, type SF" 2 } } */
+/* { dg-final { scan-assembler-times "load fusion, type DF" 1 } } */
+/* { dg-final { scan-assembler-times "store fusion, type SF" 2 } } */
+/* { dg-final { scan-assembler-times "store fusion, type DF" 1 } } */
Index: gcc/testsuite/gcc.target/powerpc/fusion.c
===
--- gcc/testsuite/gcc.target/powerpc/fusion.c (revision 233220)
+++ gcc/testsuite/gcc.target/powerpc/fusion.c (working copy)
@@ -1,17 +1,28 @@
-/* { dg-do compile { target { powerpc*-*-* } } } */
+/* { dg-do compile { target { powerpc*-*-* && lp64 } } } */
/* { dg-skip-if "" { powerpc*-*-darwin* } { "*" } { "" } } */
/* { dg-require-effective-target powerpc_p8vector_ok } */
/* { dg-skip-if "do not override -mcpu" { powerpc*-*-* } { "-mcpu=*" } {
"-mcpu=power7" } } */
-/* { dg-options "-mcpu=power7 -mtune=power8 -O3" } */
+/* { dg-options "-mcpu=power7 -mtune=power8 -O3 -mcmodel=medium" } */
-#define LARGE 0x12345
+#define SIZE 4
+struct foo {
+ unsigned char uc;
+ signed char sc;
+ unsigned short us;
+ short ss;
+ int i;
+ unsigned u;
+};
-int fusion_uchar (unsigned char *p){ return p[LARGE]; }
-int fusion_schar
