The FP load and test instruction should not be used for a comparison if
the target operand is being used afterwards. It unfortunately turns
SNaNs into QNaNs.
Bootstrapped and regression tested on s390x.
gcc/ChangeLog:
2017-03-17 Andreas Krebbel <kreb...@linux.vnet.ibm.com>
* config/s390/s390.md ("cmp<mode>_ccs_0"): Add a clobber of the
target operand. A new splitter adds the clobber statement in case
the target operand is dead anyway.
gcc/testsuite/ChangeLog:
2017-03-17 Andreas Krebbel <kreb...@linux.vnet.ibm.com>
* gcc.target/s390/load-and-test-fp-1.c: New test.
* gcc.target/s390/load-and-test-fp-2.c: New test.
---
gcc/config/s390/s390.md | 27 ++++++++++++++++++++--
gcc/testsuite/gcc.target/s390/load-and-test-fp-1.c | 17 ++++++++++++++
gcc/testsuite/gcc.target/s390/load-and-test-fp-2.c | 16 +++++++++++++
3 files changed, 58 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/s390/load-and-test-fp-1.c
create mode 100644 gcc/testsuite/gcc.target/s390/load-and-test-fp-2.c
diff --git a/gcc/config/s390/s390.md b/gcc/config/s390/s390.md
index 164a644..19daf31 100644
--- a/gcc/config/s390/s390.md
+++ b/gcc/config/s390/s390.md
@@ -1284,16 +1284,39 @@
; (TF|DF|SF|TD|DD|SD) instructions
+
+; load and test instructions turn SNaN into QNaN what is not
+; acceptable if the target will be used afterwards. On the other hand
+; they are quite convenient for implementing comparisons with 0.0. So
+; try to enable them via splitter if the value isn't needed anymore.
+
; ltxbr, ltdbr, ltebr, ltxtr, ltdtr
(define_insn "*cmp<mode>_ccs_0"
[(set (reg CC_REGNUM)
- (compare (match_operand:FP 0 "register_operand" "f")
- (match_operand:FP 1 "const0_operand" "")))]
+ (compare (match_operand:FP 0 "register_operand" "f")
+ (match_operand:FP 1 "const0_operand" "")))
+ (clobber (match_operand:FP 2 "register_operand" "=0"))]
"s390_match_ccmode(insn, CCSmode) && TARGET_HARD_FLOAT"
"lt<xde><bt>r\t%0,%0"
[(set_attr "op_type" "RRE")
(set_attr "type" "fsimp<mode>")])
+(define_split
+ [(set (match_operand 0 "cc_reg_operand")
+ (compare (match_operand:FP 1 "register_operand")
+ (match_operand:FP 2 "const0_operand")))]
+ "TARGET_HARD_FLOAT && REG_P (operands[1]) && dead_or_set_p (insn,
operands[1])"
+ [(parallel
+ [(set (match_dup 0) (match_dup 3))
+ (clobber (match_dup 1))])]
+ {
+ /* s390_match_ccmode requires the compare to have the same CC mode
+ as the CC destination register. */
+ operands[3] = gen_rtx_COMPARE (GET_MODE (operands[0]),
+ operands[1], operands[2]);
+ })
+
+
; cxtr, cxbr, cdtr, cdbr, cebr, cdb, ceb
(define_insn "*cmp<mode>_ccs"
[(set (reg CC_REGNUM)
diff --git a/gcc/testsuite/gcc.target/s390/load-and-test-fp-1.c
b/gcc/testsuite/gcc.target/s390/load-and-test-fp-1.c
new file mode 100644
index 0000000..b9d5912
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/load-and-test-fp-1.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -mzarch" } */
+
+/* a is used after the comparison. We cannot use load and test here
+ since it would turn SNaNs into QNaNs. */
+
+double gl;
+
+double
+foo (double dummy, double a)
+{
+ if (a == 0.0)
+ gl = 1;
+ return a;
+}
+
+/* { dg-final { scan-assembler "cdbr\t" } } */
diff --git a/gcc/testsuite/gcc.target/s390/load-and-test-fp-2.c
b/gcc/testsuite/gcc.target/s390/load-and-test-fp-2.c
new file mode 100644
index 0000000..7646fdd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/load-and-test-fp-2.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+/* a is not used after the comparison. So we should use load and test
+ here. */
+
+double gl;
+
+void
+bar (double a)
+{
+ if (a == 0.0)
+ gl = 1;
+}
+
+/* { dg-final { scan-assembler "ltdbr\t" } } */
--
2.9.1
