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