i386.c (ix86_epilogue): For pentium processors...

        * i386.c (ix86_epilogue): For pentium processors, try to deallocate
        4 or 8 byte stacks with pop instructions instead of an add instruction.

From-SVN: r20979

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b95a7928eb01cfeb20f169d3bfb8a7b876979eb7..83eaeac326a21dbc7326b39d9a6839f8bb0b9300 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+Tue Jul  7 00:36:41 1998  Ulrich Drepper <drepper@cygnus.com>
+
+       * i386.c (ix86_epilogue): For pentium processors, try to deallocate
+       4 or 8 byte stacks with pop instructions instead of an add instruction.
+
 Tue Jul  7 00:30:08 1998  Klaus Kaempf <kkaempf@rmi.de>
 
        * alpha.c: Include tree.h before expr.h.

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 45612c71a7ed004cf3126189688f9157a77af5e8..42c4dbbe2bc77a16c29be7ee7b6a8feab9550aab 100644 (file)
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -2353,14 +2353,57 @@ ix86_epilogue (do_rtl)
 
   else if (tsize)
     {
-      /* If there is no frame pointer, we must still release the frame. */
-      xops[0] = GEN_INT (tsize);
+      /* Intel's docs say that for 4 or 8 bytes of stack frame one should
+        use `pop' and not `add'.  */
+      int use_pop = tsize == 4;
 
-      if (do_rtl)
-       emit_insn (gen_rtx (SET, VOIDmode, xops[2],
-                           gen_rtx (PLUS, SImode, xops[2], xops[0])));
+      /* Use two pops only for the Pentium processors.  */
+      if (tsize == 8 && !TARGET_386 && !TARGET_486)
+       {
+         rtx retval = current_function_return_rtx;
+
+         xops[1] = gen_rtx_REG (SImode, 1);    /* %edx */
+
+         /* This case is a bit more complex.  Since we cannot pop into
+            %ecx twice we need a second register.  But this is only
+            available if the return value is not of DImode in which
+            case the %edx register is not available.  */
+         use_pop = (retval == NULL
+                    || ! reg_overlap_mentioned_p (xops[1], retval));
+       }
+
+      if (use_pop)
+       {
+         xops[0] = gen_rtx_REG (SImode, 2);    /* %ecx */
+
+         if (do_rtl)
+           {
+             /* We have to prevent the two pops here from being scheduled.
+                GCC otherwise would try in some situation to put other
+                instructions in between them which has a bad effect.  */
+             emit_insn (gen_blockage ());
+             emit_insn (gen_pop (xops[0]));
+             if (tsize == 8)
+               emit_insn (gen_pop (xops[1]));
+           }
+         else
+           {
+             output_asm_insn ("pop%L0 %0", xops);
+             if (tsize == 8)
+               output_asm_insn ("pop%L1 %1", xops);
+           }
+       }
       else
-       output_asm_insn (AS2 (add%L2,%0,%2), xops);
+       {
+         /* If there is no frame pointer, we must still release the frame. */
+         xops[0] = GEN_INT (tsize);
+
+         if (do_rtl)
+           emit_insn (gen_rtx (SET, VOIDmode, xops[2],
+                               gen_rtx (PLUS, SImode, xops[2], xops[0])));
+         else
+           output_asm_insn (AS2 (add%L2,%0,%2), xops);
+       }
     }
 
 #ifdef FUNCTION_BLOCK_PROFILER_EXIT