Hi,
The enclosed testcase fails on x86 when compiled with -Os since we pass
a byte parameter with a byte load in caller and read it as an int in
callee. The reason it only shows up with -Os is x86 backend encodes
a byte load with an int load if -O isn't used. When a byte load is
used, the upper 24 bits of the register have random value for none
WORD_REGISTER_OPERATIONS targets.
It happens because setup_incoming_promotions in combine.c has
/* The mode and signedness of the argument before any promotions happen
(equal to the mode of the pseudo holding it at that stage). */
mode1 = TYPE_MODE (TREE_TYPE (arg));
uns1 = TYPE_UNSIGNED (TREE_TYPE (arg));
/* The mode and signedness of the argument after any source language and
TARGET_PROMOTE_PROTOTYPES-driven promotions. */
mode2 = TYPE_MODE (DECL_ARG_TYPE (arg));
uns3 = TYPE_UNSIGNED (DECL_ARG_TYPE (arg));
/* The mode and signedness of the argument as it is actually passed,
after any TARGET_PROMOTE_FUNCTION_ARGS-driven ABI promotions. */
mode3 = promote_function_mode (DECL_ARG_TYPE (arg), mode2, &uns3,
TREE_TYPE (cfun->decl), 0);
while they are actually passed in register by assign_parm_setup_reg in
function.c:
/* Store the parm in a pseudoregister during the function, but we may
need to do it in a wider mode. Using 2 here makes the result
consistent with promote_decl_mode and thus expand_expr_real_1. */
promoted_nominal_mode
= promote_function_mode (data->nominal_type, data->nominal_mode, &unsignedp,
TREE_TYPE (current_function_decl), 2);
where nominal_type and nominal_mode are set up with TREE_TYPE (parm)
and TYPE_MODE (nominal_type). TREE_TYPE here is
(gdb) call debug_tree (type)
<enumeral_type 0x7ffff19f85e8 X
type <integer_type 0x7ffff18a93f0 unsigned char public unsigned
string-flag QI
size <integer_cst 0x7ffff18a5fa8 constant 8>
unit size <integer_cst 0x7ffff18a5fc0 constant 1>
align 8 symtab 0 alias set -1 canonical type 0x7ffff18a93f0
precision 8 min <integer_cst 0x7ffff18a5fd8 0> max <integer_cst
0x7ffff18a5f78 255>>
static unsigned type_5 QI size <integer_cst 0x7ffff18a5fa8 8> unit
size <integer_cst 0x7ffff18a5fc0 1>
align 8 symtab 0 alias set -1 canonical type 0x7ffff19f85e8
precision 8 min <integer_cst 0x7ffff18a5fd8 0> max <integer_cst
0x7ffff18a5f78 255>
values <tree_list 0x7ffff19fb028
purpose <identifier_node 0x7ffff19f6738 V
bindings <(nil)>
local bindings <(nil)>>
value <const_decl 0x7ffff18c21c0 V type <enumeral_type
0x7ffff19f85e8 X>
readonly constant used VOID file pr64037.ii line 2 col 3
align 1 context <enumeral_type 0x7ffff19f85e8 X> initial
<integer_cst 0x7ffff19d8d08 2>>> context <translation_unit_decl
0x7ffff7ff91e0 D.1>
chain <type_decl 0x7ffff19f5c78 X>>
(gdb)
and DECL_ARG_TYPE is
(gdb) call debug_tree (type)
<integer_type 0x7ffff18a9690 int public SI
size <integer_cst 0x7ffff18a5e70 type <integer_type 0x7ffff18a9150
bitsizetype> constant 32>
unit size <integer_cst 0x7ffff18a5e88 type <integer_type
0x7ffff18a90a8 sizetype> constant 4>
align 32 symtab 0 alias set 1 canonical type 0x7ffff18a9690
precision 32 min <integer_cst 0x7ffff18c60c0 -2147483648> max
<integer_cst 0x7ffff18c60d8 2147483647>
pointer_to_this <pointer_type 0x7ffff18cb930>>
(gdb)
This mismatch makes combine thinks a byte parameter is passed as int
in register and turns
(insn 9 6 10 2 (set (reg:SI 92 [ b ])
(zero_extend:SI (subreg:QI (reg:SI 91 [ b ]) 0))) pr64037.ii:9
138 {*zero_extendqisi2}
(expr_list:REG_DEAD (reg:SI 91 [ b ])
(nil)))
(insn 10 9 0 2 (set (mem:SI (reg/v/f:SI 88 [ out ]) [1 *out_4(D)+0 S4
A32])
(reg:SI 92 [ b ])) pr64037.ii:9 90 {*movsi_internal}
(expr_list:REG_DEAD (reg:SI 92 [ b ])
(expr_list:REG_DEAD (reg/v/f:SI 88 [ out ])
(nil))))
into
Trying 9 -> 10:
Successfully matched this instruction:
(set (mem:SI (reg/v/f:SI 88 [ out ]) [1 *out_4(D)+0 S4 A32])
(reg:SI 91 [ b ]))
allowing combination of insns 9 and 10
original costs 6 + 4 = 10
replacement cost 4
deferring deletion of insn with uid = 9.
modifying insn i3 10: [r88:SI]=r91:SI
REG_DEAD r91:SI
REG_DEAD r88:SI
This patch makes setup_incoming_promotions to match assign_parm_setup_reg.
Tested on Linux/x86-64 without regressions. OK for trunk and backport?
Thanks.
H.J.
----
diff --git a/gcc/combine.c b/gcc/combine.c
index 1808f97..a0449a2 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -1561,8 +1561,8 @@ setup_incoming_promotions (rtx_insn *first)
uns3 = TYPE_UNSIGNED (DECL_ARG_TYPE (arg));
/* The mode and signedness of the argument as it is actually passed,
- after any TARGET_PROMOTE_FUNCTION_ARGS-driven ABI promotions. */
- mode3 = promote_function_mode (DECL_ARG_TYPE (arg), mode2, &uns3,
+ see assign_parm_setup_reg in function.c. */
+ mode3 = promote_function_mode (TREE_TYPE (arg), mode1, &uns1,
TREE_TYPE (cfun->decl), 0);
/* The mode of the register in which the argument is being passed. */
diff --git a/gcc/testsuite/g++.dg/pr64037.C b/gcc/testsuite/g++.dg/pr64037.C
new file mode 100644
index 0000000..e5cd0e2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr64037.C
@@ -0,0 +1,27 @@
+// { dg-do run { target i?86-*-* x86_64-*-* } }
+// { dg-options "-std=c++11 -Os" }
+
+enum class X : unsigned char {
+ V = 2,
+};
+
+static void
+__attribute__((noinline,noclone))
+foo(unsigned &out, unsigned a, X b)
+{
+ out = static_cast<unsigned>(b);
+}
+
+int main()
+{
+ unsigned deadbeef = 0xDEADBEEF;
+ asm volatile ("" : "+d" (deadbeef), "+c" (deadbeef));
+
+ unsigned out;
+ foo(out, 2, X::V);
+
+ if (out != 2)
+ __builtin_abort ();
+
+ return 0;
+}
