[PATCH] Saner return value for gen_lowpart_no_emit

[PATCH] Saner return value for gen_lowpart_no_emit

[Paolo Bonzini]

For some reason, when I "invented" gen_lowpart_no_emit I defaulted it
to returning the original value of X.  Since gen_lowpart_no_emit is
mostly used to return simplifications, the correct thing to return when
conversion fails is NULL.  As a follow-up, every use in simplify-rtx.c
could be changed to try other simplifications if gen_lowpart_no_emit
fails; for now, I'm just avoiding a NULL pointer dereference.

2011-07-25  Paolo Bonzini  <bonzini@gnu.org>

        * rtlhooks.c (gen_lowpart_no_emit_general): Remove.
        * rtlhooks-def.h (gen_lowpart_no_emit_general): Remove prototype.
        (RTL_HOOKS_GEN_LOWPART_NO_EMIT): Default to gen_lowpart_if_possible.

Index: rtlhooks.c
===================================================================
--- rtlhooks.c	(revision 169877)
+++ rtlhooks.c	(working copy)
@@ -80,18 +80,6 @@ gen_lowpart_general (enum machine_mode m
     }
 }
 
-/* Similar to gen_lowpart, but cannot emit any instruction via
-   copy_to_reg or force_reg.  Mainly used in simplify-rtx.c.  */
-rtx
-gen_lowpart_no_emit_general (enum machine_mode mode, rtx x)
-{
-  rtx result = gen_lowpart_if_possible (mode, x);
-  if (result)
-    return result;
-  else
-    return x;
-}
-
 rtx
 reg_num_sign_bit_copies_general (const_rtx x ATTRIBUTE_UNUSED,
 				 enum machine_mode mode ATTRIBUTE_UNUSED,
Index: rtlhooks-def.h
===================================================================
--- rtlhooks-def.h	(revision 169877)
+++ rtlhooks-def.h	(working copy)
@@ -23,7 +23,7 @@ along with GCC; see the file COPYING3.  
 #include "rtl.h"
 
 #define RTL_HOOKS_GEN_LOWPART gen_lowpart_general
-#define RTL_HOOKS_GEN_LOWPART_NO_EMIT gen_lowpart_no_emit_general
+#define RTL_HOOKS_GEN_LOWPART_NO_EMIT gen_lowpart_if_possible
 #define RTL_HOOKS_REG_NONZERO_REG_BITS reg_nonzero_bits_general
 #define RTL_HOOKS_REG_NUM_SIGN_BIT_COPIES reg_num_sign_bit_copies_general
 #define RTL_HOOKS_REG_TRUNCATED_TO_MODE reg_truncated_to_mode_general
@@ -38,7 +38,6 @@ along with GCC; see the file COPYING3.  
 }
 
 extern rtx gen_lowpart_general (enum machine_mode, rtx);
-extern rtx gen_lowpart_no_emit_general (enum machine_mode, rtx);
 extern rtx reg_nonzero_bits_general (const_rtx, enum machine_mode, const_rtx,
 				     enum machine_mode,
 				     unsigned HOST_WIDE_INT,
Index: simplify-rtx.c
===================================================================
--- simplify-rtx.c	(revision 169877)
+++ simplify-rtx.c	(working copy)
@@ -1039,6 +1039,8 @@ simplify_unary_operation_1 (enum rtx_cod
 	    {
 	      rtx inner =
 		rtl_hooks.gen_lowpart_no_emit (tmode, XEXP (XEXP (op, 0), 0));
+              if (!inner)
+                return NULL_RTX;
 	      return simplify_gen_unary (GET_CODE (op) == ASHIFTRT
 					 ? SIGN_EXTEND : ZERO_EXTEND,
 					 mode, inner, tmode);
@@ -1092,6 +1094,8 @@ simplify_unary_operation_1 (enum rtx_cod
 	    {
 	      rtx inner =
 		rtl_hooks.gen_lowpart_no_emit (tmode, XEXP (XEXP (op, 0), 0));
+              if (!inner)
+                return NULL_RTX;
 	      return simplify_gen_unary (ZERO_EXTEND, mode, inner, tmode);
 	    }
 	}
@@ -2768,6 +2772,8 @@ simplify_binary_operation_1 (enum rtx_co
 	  if (trueop1 == constm1_rtx)
 	    {
 	      rtx x = rtl_hooks.gen_lowpart_no_emit (mode, op0);
+              if (!x)
+                return NULL_RTX;
 	      return simplify_gen_unary (NEG, mode, x, mode);
 	    }
 	}

Re: [PATCH] Saner return value for gen_lowpart_no_emit

[Richard Sandiford]

Paolo Bonzini <bonzini@gnu.org> writes:
> For some reason, when I "invented" gen_lowpart_no_emit I defaulted it
> to returning the original value of X.  Since gen_lowpart_no_emit is
> mostly used to return simplifications, the correct thing to return when
> conversion fails is NULL.  As a follow-up, every use in simplify-rtx.c
> could be changed to try other simplifications if gen_lowpart_no_emit
> fails; for now, I'm just avoiding a NULL pointer dereference.
>
> 2011-07-25  Paolo Bonzini  <bonzini@gnu.org>
>
>         * rtlhooks.c (gen_lowpart_no_emit_general): Remove.
>         * rtlhooks-def.h (gen_lowpart_no_emit_general): Remove prototype.
>         (RTL_HOOKS_GEN_LOWPART_NO_EMIT): Default to gen_lowpart_if_possible.

OK, thanks.

Richard