ICE: Global initializer should be constant!

[isanbard]

Bugzilla Link	1641
Resolution	FIXED
Resolved on	Mar 06, 2010 14:07
Version	trunk
OS	All
CC	@asl

Extended Description

This program:

struct A {
unsigned long l;
};

static void bork() {
const unsigned long vcgt = 'vcgt';
struct A a = { vcgt };
}
void foo() {
bork();
}

Compiles under GCC but gives this error for LLVM-GCC:

$ llvm-gcc -arch ppc -Os -c testcase.i
Assertion failed: ((TREE_CONSTANT(DECL_INITIAL(decl)) || TREE_CODE(DECL_INITIAL(decl)) == STRING_CST) && "Global initializer should be constant!"), function emit_global_to_llvm, file ../../llvm-gcc-4.0.src/gcc/llvm-backend.cpp, line 777.
testcase.i: In function 'foo':
testcase.i:9: internal compiler error: Abort trap
Please submit a full bug report,
with preprocessed source if appropriate.
See URL:http://llvm.org/bugs for instructions.

[isanbard]

Tree dump:

(gdb) p debug_tree(decl)
<var_decl 0x41e7b180 C.0
type <record_type 0x41e74b80 A sizes-gimplified type_0 SI
size <integer_cst 0x41e00600 constant invariant 32>
unit size <integer_cst 0x41e00120 constant invariant 4>
align 32 symtab 3 alias set -1
fields <field_decl 0x41e74c80 l type <integer_type 0x41e05600 long unsigned int>
unsigned asm-frame-size 0 SI file testcase.i line 2 size <integer_cst 0x41e00600 32> unit size
<integer_cst 0x41e00120 4>
align 32 offset_align 128
offset <integer_cst 0x41e00150 constant invariant 0>
bit offset <integer_cst 0x41e00d20 constant invariant 0> context <record_type 0x41e74b80 A> arguments <integer_cst 0x41e00150 0>
LLVM: i32 0> context <translation_unit_decl 0x41e7b580 D.1175>
LLVM: %struct.A
chain <type_decl 0x41e74c00 D.1166>>
readonly asm_written used static ignored asm-frame-size 0 SI file testcase.i line 7 size <integer_cst 0x41e00600 32> unit size <integer_cst 0x41e00120
4>
align 32 context <function_decl 0x41e74d80 bork> initial <constructor 0x41e12a20>
LLVM: %struct.A* @​C.0.1172 chain <var_decl 0x41e7b000 vcgt>>
cc1(83428) malloc: *** mmap(size=4294918144) failed (error code=12)
*** error: can't allocate region
*** set a breakpoint in malloc_error_break to debug

???^P\223 \201?: out of memory allocating 4294917248 bytes after a total of 0 bytes

Program exited with code 01.
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on"
Evaluation of the expression containing the function (debug_tree) will be abandoned.

[isanbard]

Seems to affect PPC only...

[isanbard]

The vcgt variable:

(gdb) p debug_tree(0x41e7b000)
<var_decl 0x41e7b000 vcgt
type <integer_type 0x41e74f80 long unsigned int readonly sizes-gimplified unsigned SI
size <integer_cst 0x41e00600 constant invariant 32>
unit size <integer_cst 0x41e00120 constant invariant 4>
align 32 symtab 0 alias set -1 precision 32 min <integer_cst 0x41e007b0 0> max <integer_cst 0x41e00780 4294967295>>
readonly used unsigned asm-frame-size 0 SI file testcase.i line 6 size <integer_cst 0x41e00600 32> unit size <integer_cst 0x41e00120 4>
align 32 context <function_decl 0x41e74d80 bork> chain <var_decl 0x41e7b080 a>>
cc1(83440) malloc: *** mmap(size=4294918144) failed (error code=12)
*** error: can't allocate region
*** set a breakpoint in malloc_error_break to debug

???^P\223 \201?: out of memory allocating 4294917248 bytes after a total of 0 bytes

Program exited with code 01.
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on"
Evaluation of the expression containing the function (debug_tree) will be abandoned.

[isanbard]

Results of debug_tree(DECL_INITIAL(decl)):

<constructor 0x41e12a20
type <record_type 0x41e74b80 A sizes-gimplified type_0 SI
size <integer_cst 0x41e00600 constant invariant 32>
unit size <integer_cst 0x41e00120 constant invariant 4>
align 32 symtab 3 alias set -1
fields <field_decl 0x41e74c80 l type <integer_type 0x41e05600 long unsigned int>
unsigned asm-frame-size 0 SI file testcase.i line 2 size <integer_cst 0x41e00600 32> unit size <integer_cst 0x41e00120 4>
align 32 offset_align 128
offset <integer_cst 0x41e00150 constant invariant 0>
bit offset <integer_cst 0x41e00d20 constant invariant 0> context <record_type 0x41e74b80 A> arguments <integer_cst 0x41e00150 0>
LLVM: i32 0> context <translation_unit_decl 0x41e7b580 D.1175>
LLVM: %struct.A
chain <type_decl 0x41e74c00 D.1166>>

arg 0 <tree_list 0x41e7a5c0 purpose <field_decl 0x41e74c80 l>
    value <integer_cst 0x41e12960 constant invariant 1986226036>>>

[isanbard]

Now it's failing on x86.

Results of debug_tree(DECL_INITIAL(decl)):

<constructor 0x41e10660
type <record_type 0x41e61500 A sizes-gimplified type_0 SI
size <integer_cst 0x41e006c0 constant invariant 32>
unit size <integer_cst 0x41e001e0 constant invariant 4>
align 32 symtab 3 alias set -1
fields <field_decl 0x41e61600 l type <integer_type 0x41e05700 long unsigned int>
unsigned asm-frame-size 0 SI file z.c line 2 size <integer_cst 0x41e006c0 32> unit size <integer_cst 0x41e001e0 4>
align 32 offset_align 128
offset <integer_cst 0x41e00210 constant invariant 0>
bit offset <integer_cst 0x41e00de0 constant invariant 0> context <record_type 0x41e61500 A> arguments <integer_cst 0x41e00210 0>
LLVM: i32 0> context <translation_unit_decl 0x41e61f00 D.941>
LLVM: %struct.A
chain <type_decl 0x41e61580 D.932>>

arg 0 <tree_list 0x41e69900 purpose <field_decl 0x41e61600 l>
    value <integer_cst 0x41e105a0 constant invariant 1986226036>>>

[isanbard]

Stack trace:

#​0 emit_global_to_llvm (decl=0x41e7b180) at ../../llvm-gcc-4.0.src/gcc/llvm-backend.cpp:776
#​1 0x003bd664 in rest_of_decl_compilation (decl=0x41e7b180, top_level=0, at_end=0) at ../../llvm-gcc-4.0.src/gcc/passes.c:252
#​2 0x003f8374 in TreeToLLVM::EmitBIND_EXPR (this=0xbfffed58, exp=0x41e12cf0, DestLoc=0x0) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:1621
#​3 0x003e72b4 in TreeToLLVM::Emit (this=0xbfffed58, exp=0x41e12cf0, DestLoc=0x0) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:784
#​4 0x003f7774 in TreeToLLVM::EmitSTATEMENT_LIST (this=0xbfffed58, exp=<value temporarily unavailable, due to optimizations>, DestLoc=<value temporarily u
navailable, due to optimizations>) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:1657
#​5 0x003e72c8 in TreeToLLVM::Emit (this=0xbfffed58, exp=0x41e7a680, DestLoc=0x0) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:785
#​6 0x003f8460 in TreeToLLVM::EmitBIND_EXPR (this=0xbfffed58, exp=0x41e12cc0, DestLoc=0x0) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:1632
#​7 0x003e72b4 in TreeToLLVM::Emit (this=0xbfffed58, exp=0x41e12cc0, DestLoc=0x0) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:784
#​8 0x003f7774 in TreeToLLVM::EmitSTATEMENT_LIST (this=0xbfffed58, exp=<value temporarily unavailable, due to optimizations>, DestLoc=<value temporarily u
navailable, due to optimizations>) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:1657
#​9 0x003e72c8 in TreeToLLVM::Emit (this=0xbfffed58, exp=0x41e7a540, DestLoc=0x0) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:785
#​10 0x003f8460 in TreeToLLVM::EmitBIND_EXPR (this=0xbfffed58, exp=0x41e12bd0, DestLoc=0x0) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:1632
#​11 0x003e72b4 in TreeToLLVM::Emit (this=0xbfffed58, exp=0x41e12bd0, DestLoc=0x0) at ../../llvm-gcc-4.0.src/gcc/llvm-convert.cpp:784
#​12 0x003cd7c0 in llvm_emit_code_for_current_function (fndecl=0x41e7b280) at ../../llvm-gcc-4.0.src/gcc/llvm-backend.cpp:569
#​13 0x000b64d8 in tree_rest_of_compilation (fndecl=0x41e7b280) at ../../llvm-gcc-4.0.src/gcc/tree-optimize.c:706
#​14 0x00020984 in c_expand_body (fndecl=0x41e7b280) at ../../llvm-gcc-4.0.src/gcc/c-decl.c:6959
#​15 0x004582ac in cgraph_expand_function (node=0x41e7b500) at ../../llvm-gcc-4.0.src/gcc/cgraphunit.c:896
#​16 0x0045a518 in cgraph_optimize () at ../../llvm-gcc-4.0.src/gcc/cgraphunit.c:1812
#​17 0x00023504 in c_write_global_declarations () at ../../llvm-gcc-4.0.src/gcc/c-decl.c:7965
#​18 0x00389eb0 in toplev_main (argc=<value temporarily unavailable, due to optimizations>, argv=<value temporarily unavailable, due to optimizations>) at
../../llvm-gcc-4.0.src/gcc/toplev.c:1113
#​19 0x00002594 in unload_deplibs (handle=0x1) at ltdl.c:2991

[isanbard]

Results of -fdump-tree-all:

z.c.t03.generic:
bork ()
{
static struct A C.0 = {.l=1986226036};
const long unsigned int vcgt;
struct A a;

vcgt = 1986226036;
a = C.0;
}

foo ()
{
bork ();
}

z.c.t02.original:

;; Function bork (bork)
;; enabled by -tree-original

{
const long unsigned int vcgt = 1986226036;
struct A a = {.l=1986226036};

<STATEMENT_LIST>
}

;; Function foo (foo)
;; enabled by -tree-original

{
bork ();
}

[asl]

Seems something funny during gimplification. I'm having here:

bork ()
{
const long unsigned int vcgt;
struct A a;

vcgt = 1986226036;
a.l = vcgt;
}

[asl]

The "suspicious" stuff is "apple local" in gimplify_init_constructor().

[isanbard]

This happens for "assert" builds. It's not machine specific. A constructor node is marked as non-constant but has all constant values.

[asl]

Ok. It seems we've found the issue.

1. It's only seen at -O due to constfold in the frontend
2. Either assertion is not always valid or tree is somehow bogus: we're seeing CONSTRUCTOR node, which is not marked is constant, but its "value" is integer constant.

[isanbard]

I worked with Mike at work here, and he came up with this patch. It appears to work. I would like people's opinions on it. The reasoning behind this patch is that it's valid (and, indeed, correct) for the front end to mark a variable as non-constant if it's used as a constructor. Even if it's marked with a "const" modifier. But if we know that it's initialized with a constant, then we can mark it as constant in the FE. This does that. It even worked in the recursive case.

What do you think?

Index: gcc/c-typeck.c

--- gcc/c-typeck.c (revision 41730)
+++ gcc/c-typeck.c (working copy)
@@ -6157,8 +6157,14 @@

if (value == error_mark_node)
constructor_erroneous = 1;

• else if (!TREE_CONSTANT (value))
• constructor_constant = 0;

• else if (!(TREE_CONSTANT (value)

•         || (DECL_P (value)
  

•             && DECL_INITIAL (value)
  

•             && DECL_INITIAL (value) != error_mark_node
  

•             && ! TREE_THIS_VOLATILE (value)
  

•             && ! TYPE_P (DECL_INITIAL (value))
  

•             && TREE_CONSTANT (DECL_INITIAL (value)))))
  

• constructor_constant = 0;
  else if (!initializer_constant_valid_p (value, TREE_TYPE (value))
  || ((TREE_CODE (constructor_type) == RECORD_TYPE
  || TREE_CODE (constructor_type) == UNION_TYPE)

[isanbard]

Fixed:

http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070903/053310.html

-bw

[matthijskooijman]

mentioned in issue llvm/llvm-bugzilla-archive#2452