S/390: PR78857: Don't use load and test if result is live.

Message ID 20170317140833.22002-1-krebbel@linux.vnet.ibm.com
State New
Headers show

Commit Message

Andreas Krebbel March 17, 2017, 2:08 p.m.
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  <krebbel@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  <krebbel@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

Patch

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" } } */