Hi!
The following testcase is miscompiled on ia32 at -O2, because
when expand_SPACESHIP is called, we have pending stack adjustment
from the foo call right before it.
Now, ix86_expand_fp_spaceship uses emit_jump_insn several times
but then emit_jump also several times. While emit_jump_insn doesn't
do do_pending_stack_adjust (), emit_jump does, so we end up with:
...
8: call [`_Z3foodl'] argc:0x10
REG_CALL_DECL `_Z3foodl'
9: r88:DF=[`a']
10: r89:HI=unspec[cmp(r88:DF,0.0)] 25
11: flags:CC=unspec[r89:HI] 26
12: pc={(unordered(flags:CCFP,0))?L27:pc}
REG_BR_PROB 536868
66: NOTE_INSN_BASIC_BLOCK 4
13: pc={(uneq(flags:CCFP,0))?L19:pc}
REG_BR_PROB 214748364
67: NOTE_INSN_BASIC_BLOCK 5
14: pc={(flags:CCFP>0)?L23:pc}
REG_BR_PROB 536870916
68: NOTE_INSN_BASIC_BLOCK 6
15: r86:SI=0xffffffffffffffff
16: {sp:SI=sp:SI+0x10;clobber flags:CC;}
REG_ARGS_SIZE 0
17: pc=L29
18: barrier
19: L19:
69: NOTE_INSN_BASIC_BLOCK 7
...
The sp += 16 pending stuck adjust was emitted in the middle of the
sequence and is effective only for the single case of the 4 possibilities
where .SPACESHIP returns -1, in all other cases the stack isn't adjusted
and so we ICE during dwarf2cfi.
Now, we could either call do_pending_stack_adjust in
ix86_expand_fp_spaceship, or use there calls that actually don't call
do_pending_stack_adjust (but having the stack adjustment across branches is
generally undesirable), or we can call it in expand_SPACESHIP for all
targets (note, just i386 currently implements it).
I chose the generic code because e.g. expand_{addsub,neg,mul}_overflow
in the same file also call do_pending_stack_adjust in internal-fn.cc for the
same reasons, that it is expected that most if not all targets will expand
those through jumps and we don't want all of the targets to need to deal
with that.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Or do you prefer it in ix86_expand_fp_spaceship instead?
2022-02-24 Jakub Jelinek <ja...@redhat.com>
PR middle-end/104679
* internal-fn.cc (expand_SPACESHIP): Call do_pending_stack_adjust.
* g++.dg/torture/pr104679.C: New test.
--- gcc/internal-fn.cc.jj 2022-02-11 13:51:07.757597854 +0100
+++ gcc/internal-fn.cc 2022-02-24 17:46:01.476722703 +0100
@@ -4437,6 +4437,8 @@ expand_SPACESHIP (internal_fn, gcall *st
tree rhs2 = gimple_call_arg (stmt, 1);
tree type = TREE_TYPE (rhs1);
+ do_pending_stack_adjust ();
+
rtx target = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
rtx op1 = expand_normal (rhs1);
rtx op2 = expand_normal (rhs2);
--- gcc/testsuite/g++.dg/torture/pr104679.C.jj 2022-02-24 17:48:08.309959261
+0100
+++ gcc/testsuite/g++.dg/torture/pr104679.C 2022-02-24 17:48:00.226071655
+0100
@@ -0,0 +1,22 @@
+// PR middle-end/104679
+// { dg-do compile }
+
+struct A { ~A (); };
+void foo (double, long);
+void bar ();
+double a;
+long b;
+
+void
+baz ()
+{
+ foo (a, b);
+ if (a == 0.0)
+ ;
+ else
+ while (a > 0.0)
+ {
+ A c;
+ bar ();
+ }
+}
Jakub
