From: Andreas Krebbel <krebbel@linux.ibm.com>
Date: Tue, 20 Nov 2018 16:19:54 +0000 (+0000)
Subject: S/390: Fix flogr RTX.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=33f3393ab5cc809f2636cc3ce86b3032177c91b8;p=gcc.git

S/390: Fix flogr RTX.

The flogr instruction uses a 64 bit register pair target operand.  In
the RTX we model this as a write to a TImode register.  Unfortunately
the RTX's being assigned to the two parts of the target operand were
swapped.  This is no problem if in the end the flogr instruction will
be emitted since the instruction still does what the clzdi expander
expects.  However, a problem arises when the RTX is used to optimize
CLZ for a constant input operand.  Even then it matters only if the
expression couldn't be folded on tree level already.

In the testcase this happened thanks to loop unrolling on RTL level.
The iteration variable is used as an argument to the clz
builtin. Due to the loop unrolling it becomes a constant and after
folding the broken RTX leads to a wrong assumption.

gcc/ChangeLog:

2018-11-20  Andreas Krebbel  <krebbel@linux.ibm.com>

	* config/s390/s390.md ("clztidi2"): Swap the RTX's written to the
	DImode parts of the target operand.

gcc/testsuite/ChangeLog:

2018-11-20  Andreas Krebbel  <krebbel@linux.ibm.com>

	* gcc.target/s390/flogr-1.c: New test.

From-SVN: r266321
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index d9af1e50781..779ed594878 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2018-11-20  Andreas Krebbel  <krebbel@linux.ibm.com>
+
+	* config/s390/s390.md ("clztidi2"): Swap the RTX's written to the
+	DImode parts of the target operand.
+
 2018-11-20  Nathan Sidwell  <nathan@acm.org>
 
 	PR 87926
diff --git a/gcc/config/s390/s390.md b/gcc/config/s390/s390.md
index 721222d221f..30d113fd9cc 100644
--- a/gcc/config/s390/s390.md
+++ b/gcc/config/s390/s390.md
@@ -8759,17 +8759,17 @@
   DONE;
 })
 
+; CLZ result is in hard reg op0 - this is the high part of the target operand
+; The source with the left-most one bit cleared is in hard reg op0 + 1 - the low part
 (define_insn "clztidi2"
   [(set (match_operand:TI 0 "register_operand" "=d")
 	(ior:TI
-	  (ashift:TI
-            (zero_extend:TI
-   	      (xor:DI (match_operand:DI 1 "register_operand" "d")
-                      (lshiftrt (match_operand:DI 2 "const_int_operand" "")
-				(subreg:SI (clz:DI (match_dup 1)) 4))))
-
-	    (const_int 64))
-          (zero_extend:TI (clz:DI (match_dup 1)))))
+	  (ashift:TI (zero_extend:TI (clz:DI (match_operand:DI 1 "register_operand" "d")))
+		     (const_int 64))
+	  (zero_extend:TI
+	   (xor:DI (match_dup 1)
+		   (lshiftrt (match_operand:DI 2 "const_int_operand" "")
+			     (subreg:SI (clz:DI (match_dup 1)) 4))))))
    (clobber (reg:CC CC_REGNUM))]
   "UINTVAL (operands[2]) == HOST_WIDE_INT_1U << 63
    && TARGET_EXTIMM && TARGET_ZARCH"
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 4ec625f1768..d522b2cebdc 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2018-11-20  Andreas Krebbel  <krebbel@linux.ibm.com>
+
+	* gcc.target/s390/flogr-1.c: New test.
+
 2018-11-20  Jan Hubicka  <hubicka@ucw.cz>
 
 	PR ipa/87706
diff --git a/gcc/testsuite/gcc.target/s390/flogr-1.c b/gcc/testsuite/gcc.target/s390/flogr-1.c
new file mode 100644
index 00000000000..a3869000d62
--- /dev/null
+++ b/gcc/testsuite/gcc.target/s390/flogr-1.c
@@ -0,0 +1,47 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -funroll-loops -march=z9-109" } */
+/* { dg-require-effective-target stdint_types } */
+
+/* Folding of the FLOGR caused a wrong value to be returned by
+   __builtin_clz becuase of a problem in the RTX we emit for FLOGR.
+   The problematic folding can only be triggered with constants inputs
+   introduced on RTL level.  In this case it happens with loop
+   unrolling.  */
+
+#include <stdint.h>
+#include <assert.h>
+
+static inline uint32_t pow2_ceil_u32(uint32_t x) {
+  if (x <= 1) {
+    return x;
+  }
+  int msb_on_index;
+  msb_on_index = (31 ^ __builtin_clz(x - 1));
+  assert(msb_on_index < 31);
+  return 1U << (msb_on_index + 1);
+}
+
+void __attribute__((noinline,noclone))
+die (int a)
+{
+  if (a)
+    __builtin_abort ();
+}
+
+void test_pow2_ceil_u32(void) {
+  unsigned i;
+
+  for (i = 0; i < 18; i++) {
+      uint32_t a_ = (pow2_ceil_u32(((uint32_t)1) << i));
+      if (!(a_ == (((uint32_t)1) << i))) {
+	die(1);
+      }
+  }
+}
+
+int
+main(void) {
+  test_pow2_ceil_u32();
+
+  return 0;
+}