From: Segher Boessenkool <segher@kernel.crashing.org>
Date: Tue, 18 Aug 2015 14:27:50 +0000 (+0200)
Subject: re PR rtl-optimization/67028 (combine bug. Different assumptions about subreg in... 
X-Git-Tag: releases/gcc-4.9.4~643
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=360200529e482f757da09bc645b3748460b60977;p=thirdparty%2Fgcc.git

re PR rtl-optimization/67028 (combine bug. Different assumptions about subreg in different places.)

	PR rtl-optimization/67028
	* combine.c (simplify_comparison): Fix comment.  Rearrange code.
	Add test to see if a const_int fits in the new mode.

gcc/testsuite/
	PR rtl-optimization/67028
	* gcc.dg/pr67028.c: New testcase.

From-SVN: r226971
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 5959f9dab298..4fc0435cb80d 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2015-08-18  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	Backport from mainline:
+	2015-08-08  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR rtl-optimization/67028
+	* combine.c (simplify_comparison): Fix comment.  Rearrange code.
+	Add test to see if a const_int fits in the new mode.
+
 2015-08-16  Uros Bizjak  <ubizjak@gmail.com>
 
 	Backport from mainline:
diff --git a/gcc/combine.c b/gcc/combine.c
index adea2c161b62..a22aba7d48e4 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -11655,14 +11655,15 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
 	      continue;
 	    }
 
-	  /* If this is (and:M1 (subreg:M2 X 0) (const_int C1)) where C1
+	  /* If this is (and:M1 (subreg:M1 X:M2 0) (const_int C1)) where C1
 	     fits in both M1 and M2 and the SUBREG is either paradoxical
 	     or represents the low part, permute the SUBREG and the AND
 	     and try again.  */
-	  if (GET_CODE (XEXP (op0, 0)) == SUBREG)
+	  if (GET_CODE (XEXP (op0, 0)) == SUBREG
+	      && CONST_INT_P (XEXP (op0, 1)))
 	    {
-	      unsigned HOST_WIDE_INT c1;
 	      tmode = GET_MODE (SUBREG_REG (XEXP (op0, 0)));
+	      unsigned HOST_WIDE_INT c1 = INTVAL (XEXP (op0, 1));
 	      /* Require an integral mode, to avoid creating something like
 		 (AND:SF ...).  */
 	      if (SCALAR_INT_MODE_P (tmode)
@@ -11672,18 +11673,22 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1)
 		     have a defined value due to the AND operation.
 		     However, if we commute the AND inside the SUBREG then
 		     they no longer have defined values and the meaning of
-		     the code has been changed.  */
+		     the code has been changed.
+		     Also C1 should not change value in the smaller mode,
+		     see PR67028 (a positive C1 can become negative in the
+		     smaller mode, so that the AND does no longer mask the
+		     upper bits).  */
 		  && (0
 #ifdef WORD_REGISTER_OPERATIONS
 		      || (mode_width > GET_MODE_PRECISION (tmode)
-			  && mode_width <= BITS_PER_WORD)
+			  && mode_width <= BITS_PER_WORD
+			  && trunc_int_for_mode (c1, tmode) == (HOST_WIDE_INT) c1)
 #endif
 		      || (mode_width <= GET_MODE_PRECISION (tmode)
 			  && subreg_lowpart_p (XEXP (op0, 0))))
-		  && CONST_INT_P (XEXP (op0, 1))
 		  && mode_width <= HOST_BITS_PER_WIDE_INT
 		  && HWI_COMPUTABLE_MODE_P (tmode)
-		  && ((c1 = INTVAL (XEXP (op0, 1))) & ~mask) == 0
+		  && (c1 & ~mask) == 0
 		  && (c1 & ~GET_MODE_MASK (tmode)) == 0
 		  && c1 != mask
 		  && c1 != GET_MODE_MASK (tmode))
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index d90d3d7ea99d..177791878437 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2015-08-18  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	Backport from mainline:
+	2015-08-08  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR rtl-optimization/67028
+	* gcc.dg/pr67028.c: New testcase.
+
 2015-08-16  Uros Bizjak  <ubizjak@gmail.com>
 
 	Backport from mainline:
diff --git a/gcc/testsuite/gcc.dg/pr67028.c b/gcc/testsuite/gcc.dg/pr67028.c
new file mode 100644
index 000000000000..b42fb8110ebb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr67028.c
@@ -0,0 +1,21 @@
+/* { dg-do run } */
+/* { dg-options "-O3" } */
+
+short c = 0;
+
+int __attribute__ ((noinline)) f(void)
+{
+	int d = 5;
+	signed char e = (c != 1) * -2;
+	int a = (unsigned short)e > d;
+
+	return a;
+}
+
+int main(void)
+{
+	if (!f())
+		__builtin_abort();
+
+	return 0;
+}