[PATCH] Check regs_invalidated_in_call in reg_set_p

[Roger Sayle]

This patch is inspired by Zack's analysis of the comment in reg_set_p
where that function handles call clobbered registers that reads:

> We'd like to test call_used_regs here, but rtlanal.c can't
> reference that variable due to its use in genattrtab.  So
> we'll just be more conservative.

As Zack pointed out rtlanal.o isn't linked into genattrtab or any
of the gen* executables, so we can use call_used_regs.  However
investigating further I discovered that the preferred idiom for
this test is actually to use the regs_invalidated_by_call hard
reg-set.  This has the benefit over call_used_regs that it doesn't
include "fixed" registers, so that the frame pointer, for example,
isn't unconditionally considered clobbered by a function call.


The following patch has been tested on i686-pc-linux-gnu with a full
"make bootstrap", all default languages, and regression tested with a
top-level "make -k check" with no new failures.

Ok for mainline?



2004-07-18  Roger Sayle  <roger@eyesopen.com>

	* rtlanal.c (reg_set_p): Add check for regs_invalidated_by_call.


Index: rtlanal.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/rtlanal.c,v
retrieving revision 1.196
diff -c -3 -p -r1.196 rtlanal.c
*** rtlanal.c	14 Jul 2004 07:30:17 -0000	1.196
--- rtlanal.c	18 Jul 2004 19:47:56 -0000
*************** reg_set_p (rtx reg, rtx insn)
*** 941,954 ****
    if (INSN_P (insn)
        && (FIND_REG_INC_NOTE (insn, reg)
  	  || (CALL_P (insn)
- 	      /* We'd like to test call_used_regs here, but rtlanal.c can't
- 		 reference that variable due to its use in genattrtab.  So
- 		 we'll just be more conservative.
-
- 		 ??? Unless we could ensure that the CALL_INSN_FUNCTION_USAGE
- 		 information holds all clobbered registers.  */
  	      && ((REG_P (reg)
! 		   && REGNO (reg) < FIRST_PSEUDO_REGISTER)
  		  || MEM_P (reg)
  		  || find_reg_fusage (insn, CLOBBER, reg)))))
      return 1;
--- 941,950 ----
    if (INSN_P (insn)
        && (FIND_REG_INC_NOTE (insn, reg)
  	  || (CALL_P (insn)
  	      && ((REG_P (reg)
! 		   && REGNO (reg) < FIRST_PSEUDO_REGISTER
! 		   && TEST_HARD_REG_BIT (regs_invalidated_by_call,
! 					 REGNO (reg)))
  		  || MEM_P (reg)
  		  || find_reg_fusage (insn, CLOBBER, reg)))))
      return 1;

Roger
--
Roger Sayle,                         E-mail: roger@eyesopen.com
OpenEye Scientific Software,         WWW: http://www.eyesopen.com/
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