There's code in regimplification that makes us use an extra temporary
when we encounter a call returning a non-BLKmode structure. This seems
somewhat inefficient and unnecessary, and when used from the
lower-addr-spaces pass I'm working on it leads to problems further
down that look like tree-ssa bugs that I wasn't able to clearly
disentangle.
Here's what happens on compile/pr51761.c. Regimplification has the
following effect, creating an extra temporary _6:
- D.1378 = fooD.1373 (aD.1377);
+ _6 = fooD.1373 (aD.1377);
+ # .MEMD.1382 = VDEF <.MEMD.1382>
+ D.1378 = _6;
SRA turns this into:
_6 = fooD.1373 (aD.1377);
# VUSE <.MEM_3>
SR$2_7 = MEM[(struct S *)&_6];
Somehow, the address of &_6 doesn't count as a use, and the DCE pass
decides it is unused:
Eliminating unnecessary statements:
Deleting LHS of call: _6 = foo (a);
However, the statement
SR$2_7 = MEM[(struct S *)&_6];
is still present, and we have an SSA name without a definition, leading
to a crash.
Rather than figure all this out, I decided to try making the
regimplification not generate the extra copy in the first place. The
testsuite seems to agree with me that it's unnecessary. Bootstrapped and
tested on x86_64-linux, ok?
Bernd
* gimplify-me.c (gimple_regimplify_operands): Avoid unnecessary
temporary for struct returns.
diff --git a/gcc/gimplify-me.c b/gcc/gimplify-me.c
index 05eaeb0..2d1181b 100644
--- a/gcc/gimplify-me.c
+++ b/gcc/gimplify-me.c
@@ -304,25 +304,9 @@ gimple_regimplify_operands (gimple stmt, gimple_stmt_iterator *gsi_p)
need_temp = true;
}
}
- else
- {
- if (is_gimple_reg_type (TREE_TYPE (lhs)))
- need_temp = true;
- else if (TYPE_MODE (TREE_TYPE (lhs)) != BLKmode)
- {
- if (is_gimple_call (stmt))
- {
- tree fndecl = gimple_call_fndecl (stmt);
+ else if (is_gimple_reg_type (TREE_TYPE (lhs)))
+ need_temp = true;
- if (!aggregate_value_p (TREE_TYPE (lhs), fndecl)
- && !(fndecl && DECL_RESULT (fndecl)
- && DECL_BY_REFERENCE (DECL_RESULT (fndecl))))
- need_temp = true;
- }
- else
- need_temp = true;
- }
- }
if (need_temp)
{
tree temp = create_tmp_reg (TREE_TYPE (lhs), NULL);
