ssa.c (rename_insn_1): Do not wrap an assignment to a paradoxical SUBREG inside a...

        * ssa.c (rename_insn_1): Do not wrap an assignment to a
        paradoxical SUBREG inside a SEQUENCE.  Fix minor formatting
        glitch.

From-SVN: r44357

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e7b5c89f0dccde3983de2bfff4cbb4cf4ad11afc..a867ed71d888118b6f522f2625b2b5cb06ab046b 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -5,6 +5,10 @@
 
 Wed Jul 25 08:25:01 2001  Jeffrey A Law  (law@cygnus.com)
 
+       * ssa.c (rename_insn_1): Do not wrap an assignment to a 
+       paradoxical SUBREG inside a SEQUENCE.  Fix minor formatting
+       glitch.
+
        * ssa-ccp.c (visit_expression): Handle CALL_INSNs that can
        throw an exception.
        (visit_expression): When attempting to simplify an expression,

diff --git a/gcc/ssa.c b/gcc/ssa.c
index 0aeb92091f9a6abf9eb12f2ba0dd0aa11d0df8c2..770ea46902c9f3d0a9f8ea1b555c079de7dda590 100644 (file)
--- a/gcc/ssa.c
+++ b/gcc/ssa.c
@@ -833,6 +833,21 @@ rename_insn_1 (ptr, data)
        rtx *destp = &SET_DEST (x);
        rtx dest = SET_DEST (x);
 
+       /* An assignment to a paradoxical SUBREG does not read from
+          the destination operand, and thus does not need to be
+          wrapped into a SEQUENCE when translating into SSA form.
+          We merely strip off the SUBREG and proceed normally for
+          this case.  */
+       if (GET_CODE (dest) == SUBREG
+           && (GET_MODE_SIZE (GET_MODE (dest))
+               > GET_MODE_SIZE (GET_MODE (SUBREG_REG (dest))))
+           && GET_CODE (SUBREG_REG (dest)) == REG
+           && CONVERT_REGISTER_TO_SSA_P (REGNO (SUBREG_REG (dest))))
+         {
+           destp = &XEXP (dest, 0);
+           dest = XEXP (dest, 0);
+         }
+
        /* Some SETs also use the REG specified in their LHS.
           These can be detected by the presence of
           STRICT_LOW_PART, SUBREG, SIGN_EXTRACT, and ZERO_EXTRACT
@@ -842,11 +857,12 @@ rename_insn_1 (ptr, data)
           (sequence [(set (reg foo_1) (reg foo))
                      (set (subreg (reg foo_1)) ...)])  
 
-          FIXME: Much of the time this is too much.  For many libcalls,
-          paradoxical SUBREGs, etc., the input register is dead.  We should
-          recognise this in rename_block or here and not make a false
+          FIXME: Much of the time this is too much.  For some constructs
+          we know that the output register is strictly an output
+          (paradoxical SUBREGs and some libcalls for example).
+
+          For those cases we are better off not making the false
           dependency.  */
-          
        if (GET_CODE (dest) == STRICT_LOW_PART
            || GET_CODE (dest) == SUBREG
            || GET_CODE (dest) == SIGN_EXTRACT
@@ -877,8 +893,8 @@ rename_insn_1 (ptr, data)
                context->new_renames = saved_new_renames;
              }
          }
-       else if (GET_CODE (dest) == REG &&
-                CONVERT_REGISTER_TO_SSA_P (REGNO (dest)))
+       else if (GET_CODE (dest) == REG
+                && CONVERT_REGISTER_TO_SSA_P (REGNO (dest)))
          {
            /* We found a genuine set of an interesting register.  Tag
               it so that we can create a new name for it after we finish