simplify-rtx: Fix up simplify_logical_relational_operation [PR119002]

The following testcase is miscompiled on powerpc64le-linux starting with
r15-6777.  During combine we see:

(set (reg:SI 134)
    (ior:SI (ge:SI (reg:CCFP 128)
            (const_int 0 [0]))
        (lt:SI (reg:CCFP 128)
            (const_int 0 [0]))))

The simplify_logical_relational_operation code (in its current form)
was written with arithmetic rather than CC modes in mind.  Since CCFP
is a CC mode, it fails the HONOR_NANS check, and so the function assumes
that ge | lt => true.

If one comparison is unsigned then it should be safe to assume that
the other comparison is also unsigned, even for CC modes, since the
optimisation checks that the comparisons are between the same operands.
For the other cases, we can only safely fold comparisons of CC mode
values if the result is always-true (15) or always-false (0).

It turns out that the original testcase for PR117186, which ran at -O,
was relying on the old behaviour for some of the functions.  It needs
4-instruction combinations, and so -fexpensive-optimizations, to pass
in its intended form.

gcc/
	PR rtl-optimization/119002
	* simplify-rtx.cc
	(simplify_context::simplify_logical_relational_operation): Handle
	comparisons between CC values.  If there is no evidence that the
	CC values are unsigned, restrict the fold to always-true or
	always-false results.

gcc/testsuite/
	* gcc.c-torture/execute/ieee/pr119002.c: New test.
	* gcc.target/aarch64/pr117186.c: Run at -O2 rather than -O.

Co-authored-by: Jakub Jelinek <jakub@redhat.com>

diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index c478bd060fc6d6c26f9b65dec3515c89b0fd486b..fe007bc7d96a19b9ceb4d18685520a8e04e0160c 100644 (file)
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -2655,6 +2655,9 @@ simplify_context::simplify_logical_relational_operation (rtx_code code,
 
   enum rtx_code code0 = GET_CODE (op0);
   enum rtx_code code1 = GET_CODE (op1);
+  machine_mode cmp_mode = GET_MODE (XEXP (op0, 0));
+  if (cmp_mode == VOIDmode)
+    cmp_mode = GET_MODE (XEXP (op0, 1));
 
   /* Assume at first that the comparisons are on integers, and that the
      operands are therefore ordered.  */
@@ -2672,8 +2675,10 @@ simplify_context::simplify_logical_relational_operation (rtx_code code,
     }
   else
     {
-      /* See whether the operands might be unordered.  */
-      if (HONOR_NANS (GET_MODE (XEXP (op0, 0))))
+      /* See whether the operands might be unordered.  Assume that all
+        results are possible for CC modes, and punt later if we don't get an
+        always-true or always-false answer.  */
+      if (GET_MODE_CLASS (cmp_mode) == MODE_CC || HONOR_NANS (cmp_mode))
        all = 15;
       mask0 = comparison_to_mask (code0) & all;
       mask1 = comparison_to_mask (code1) & all;
@@ -2702,6 +2707,9 @@ simplify_context::simplify_logical_relational_operation (rtx_code code,
     code = mask_to_unsigned_comparison (mask);
   else
     {
+      if (GET_MODE_CLASS (cmp_mode) == MODE_CC)
+       return 0;
+
       code = mask_to_comparison (mask);
       /* LTGT and NE are arithmetically equivalent for ordered operands,
         with NE being the canonical choice.  */

diff --git a/gcc/testsuite/gcc.c-torture/execute/ieee/pr119002.c b/gcc/testsuite/gcc.c-torture/execute/ieee/pr119002.c
new file mode 100644 (file)
index 0000000..af1a705
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/ieee/pr119002.c
@@ -0,0 +1,23 @@
+/* PR rtl-optimization/119002 */
+
+__attribute__((noipa)) unsigned int
+foo (void *x, float y, float z)
+{
+  unsigned int a, b;
+  float c, d, e;
+  c = y;
+  d = z;
+  a = c < d;
+  d = y;
+  e = z;
+  b = d >= e;
+  a |= b;
+  return a;
+}
+
+int
+main ()
+{
+  if (foo ((void *) 0, 0.f, __builtin_nanf ("")))
+    __builtin_abort ();
+}

diff --git a/gcc/testsuite/gcc.target/aarch64/pr117186.c b/gcc/testsuite/gcc.target/aarch64/pr117186.c
index afe3c25a49305e7c9d69e9699f7f74057714e50a..3090f2c11d53dcd41e252461d99778f3b8653af4 100644 (file)
--- a/gcc/testsuite/gcc.target/aarch64/pr117186.c
+++ b/gcc/testsuite/gcc.target/aarch64/pr117186.c
@@ -1,4 +1,4 @@
-/* { dg-options "-O" } */
+/* { dg-options "-O2" } */
 /* { dg-final { check-function-bodies "**" "" "" } } */
 
 /*