[PATCH] simplify-rtx: Fix compare of comparisons (PR60818)

[Segher Boessenkool]

The function simplify_binary_operation_1 has code that does
/* Convert (compare (gt (flags) 0) (lt (flags) 0)) to (flags).  */
but this transformation is only valid if "flags" has the same machine
mode as the outer compare.  This fixes it.

Bootstrapped and tested on powerpc64-linux {-m32,-m64} (and tested the
new testcase with {-m32,-m64}{,-misel}).  Is this okay for trunk?


Segher


2017-03-31  Segher Boessenkool  <segher@kernel.crashing.org>

	PR rtl-optimization/60818
	* simplify-rtx.c (simplify_binary_operation_1): Do not replace
	a compare of comparisons with the thing compared if this results
	in a different machine mode.

gcc/testsuite/
	PR rtl-optimization/60818
	* gcc.c-torture/compile/pr60818.c: New testcase.

---
 gcc/simplify-rtx.c                            | 6 +++---
 gcc/testsuite/gcc.c-torture/compile/pr60818.c | 5 +++++
 2 files changed, 8 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.c-torture/compile/pr60818.c

diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 3022779..10c2800 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -2367,10 +2367,10 @@
 	      return xop00;
 
 	    if (REG_P (xop00) && REG_P (xop10)
-		&& GET_MODE (xop00) == GET_MODE (xop10)
 		&& REGNO (xop00) == REGNO (xop10)
-		&& GET_MODE_CLASS (GET_MODE (xop00)) == MODE_CC
-		&& GET_MODE_CLASS (GET_MODE (xop10)) == MODE_CC)
+		&& GET_MODE (xop00) == mode
+		&& GET_MODE (xop10) == mode
+		&& GET_MODE_CLASS (mode) == MODE_CC)
 	      return xop00;
 	}
       break;
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr60818.c b/gcc/testsuite/gcc.c-torture/compile/pr60818.c
new file mode 100644
index 0000000..b6171bb
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr60818.c
@@ -0,0 +1,5 @@
+int
+lx (int oi, int mb)
+{
+  return (oi < mb) < (mb < oi);
+}
-- 
1.9.3