combine.c (update_rsp_from_reg_equal): Only look for the nonzero bits of src in…

combine.c (update_rsp_from_reg_equal): Only look for the nonzero bits of src in nonzero_bits_mode if...

2018-12-18  Jozef Lawrynowicz  <jozef.l@mittosystems.com>

	* combine.c (update_rsp_from_reg_equal): Only look for the nonzero bits
	of src in nonzero_bits_mode if the mode of src is MODE_INT and
	HWI_COMPUTABLE.
	(reg_nonzero_bits_for_combine): Add clarification to comment.

From-SVN: r267227

gcc/ChangeLog

+2018-12-18  Jozef Lawrynowicz  <jozef.l@mittosystems.com>
+
+	* combine.c (update_rsp_from_reg_equal): Only look for the nonzero bits
+	of src in nonzero_bits_mode if the mode of src is MODE_INT and
+	HWI_COMPUTABLE.
+	(reg_nonzero_bits_for_combine): Add clarification to comment.
+
 2018-12-18  Wei Xiao  <wei3.xiao@intel.com>
 
 	* config/i386/driver-i386.c (host_detect_local_cpu): Detect cascadelake.

gcc/combine.c

@@ -1698,9 +1698,13 @@ update_rsp_from_reg_equal (reg_stat_type *rsp, rtx_insn *insn, const_rtx set,
   /* Don't call nonzero_bits if it cannot change anything.  */
   if (rsp->nonzero_bits != HOST_WIDE_INT_M1U)
     {
-      bits = nonzero_bits (src, nonzero_bits_mode);
+      machine_mode mode = GET_MODE (x);
+      if (GET_MODE_CLASS (mode) == MODE_INT
+	  && HWI_COMPUTABLE_MODE_P (mode))
+	mode = nonzero_bits_mode;
+      bits = nonzero_bits (src, mode);
       if (reg_equal && bits)
-	bits &= nonzero_bits (reg_equal, nonzero_bits_mode);
+	bits &= nonzero_bits (reg_equal, mode);
       rsp->nonzero_bits |= bits;
     }
 
@@ -10225,6 +10229,7 @@ simplify_and_const_int (rtx x, scalar_int_mode mode, rtx varop,
 
 /* Given a REG X of mode XMODE, compute which bits in X can be nonzero.
    We don't care about bits outside of those defined in MODE.
+   We DO care about all the bits in MODE, even if XMODE is smaller than MODE.
 
    For most X this is simply GET_MODE_MASK (GET_MODE (MODE)), but if X is
    a shift, AND, or zero_extract, we can do better.  */