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-[committed] Fix target/17565: asms in delay slots
-
- * From: Richard Sandiford <rsandifo at redhat dot com>
- * To: gcc-patches at gcc dot gnu dot org
- * Date: Mon, 20 Sep 2004 07:55:58 +0100
- * Subject: [committed] Fix target/17565: asms in delay slots
-
-The MIPS port was allowing asms to be put into delay slots if the
-compiler guesses they are only one instruction long. This is wrong
-because of the possibility of it containing macros.
-
-The problem can be reproduced as an assembler warning
-in the following testcase:
-
-int foo (int n)
-{
- register int k asm ("$16") = n;
- if (k > 0)
- {
- bar ();
- asm ("li %0,0x12345678" : "=r" (k));
- }
- return k;
-}
-
-because the multi-instruction asm statement goes into the delay
-slot of the call to bar().
-
-This is reduced from a much more serious linux problem. Linux is fond
-of using empty asm statements, and since gcc estimates empty asms to be
-one instruction long, they too might be put into delay slots. This
-actually has the effect of putting the following instruction into the
-delay slot instead. Since there's no assembler warning, the problem was
-only detected as a run-time failure.
-
-The fix is simple: set the asm value of "can_delay" to "no".
-Tested on mipsisa64-elf, applied to mainline.
-
-This problem goes back to at least 2.95, so it isn't technically a
-regression. On the other hand, it's the kind of bug that could trigger
-for different types of code in different releases, so I'm sure there's
-a testcase that fails (say) in 3.4 and not in 2.95. Will probably ask
-Mark for permission to backport to 3.4.
-
-Richard
-
-
- PR target/17565
- * config/mips/mips.md (define_asm_attributes): Set can_delay to no.
-
-testsuite/
- * gcc.target/mips/asm-1.c: New test.
-
-Index: config/mips/mips.md
-===================================================================
-RCS file: /cvs/gcc/gcc/gcc/config/mips/mips.md,v
-retrieving revision 1.306
-diff -c -p -F^\([(a-zA-Z0-9_]\|#define\) -r1.306 mips.md
-*** gcc/gcc/config/mips/mips.md 13 Sep 2004 19:32:05 -0000 1.306
---- gcc/gcc/config/mips/mips.md 20 Sep 2004 06:52:31 -0000
-*************** (define_attr "may_clobber_hilo" "no,yes"
-*** 266,272 ****
-
- ;; Describe a user's asm statement.
- (define_asm_attributes
-! [(set_attr "type" "multi")])
-
- ;; .........................
- ;;
---- 266,273 ----
-
- ;; Describe a user's asm statement.
- (define_asm_attributes
-! [(set_attr "type" "multi")
-! (set_attr "can_delay" "no")])
-
- ;; .........................
- ;;
-Index: testsuite/gcc.target/mips/asm-1.c
-===================================================================
-RCS file: testsuite/gcc.target/mips/asm-1.c
-diff -N testsuite/gcc.target/mips/asm-1.c
-*** gcc/gcc/testsuite/gcc.target/mips/asm-1.c 1 Jan 1970 00:00:00 -0000
---- gcc/gcc/testsuite/gcc.target/mips/asm-1.c 20 Sep 2004 06:52:31 -0000
-***************
-*** 0 ****
---- 1,14 ----
-+ /* PR target/17565. GCC used to put the asm into the delay slot
-+ of the call. */
-+ /* { dg-do assemble } */
-+ /* { dg-options "-O" } */
-+ int foo (int n)
-+ {
-+ register int k asm ("$16") = n;
-+ if (k > 0)
-+ {
-+ bar ();
-+ asm ("li %0,0x12345678" : "=r" (k));
-+ }
-+ return k;
-+ }
-