[Bug tree-optimization/43629] [4.3/4.4 Regression] Struct to register optimization fails
--- Comment #1 from rguenth at gcc dot gnu dot org 2010-04-02 11:31 ---
Confirmed. Yet another SRA to bitfield magic issue.
Workaround: -fno-tree-sra.
struct A {
short A1 ;
short A2 ;
int A3 ;
};
static struct A __attribute__((noinline))
foo(int b)
{
struct A result;
result.A1 = (short)0;
result.A2 = (short)0;
/* result.A3 is intentionally not initialized */
if (b) {
result.A1 = (short)1;
result.A2 = (short)2;
result.A3 = 3;
return result;
}
return result;
}
extern void abort (void);
int main()
{
struct A myA = foo(0);
if (myA.A1 != 0)
abort ();
return 0;
}
--
rguenth at gcc dot gnu dot org changed:
What|Removed |Added
Status|UNCONFIRMED |NEW
Component|c |tree-optimization
Ever Confirmed|0 |1
Keywords||wrong-code
Known to fail||4.3.0 4.3.4 4.4.0 4.4.3
Known to work||4.2.4 4.5.0
Last reconfirmed|-00-00 00:00:00 |2010-04-02 11:31:52
date||
Summary|Struct to register |[4.3/4.4 Regression] Struct
|optimization fails |to register optimization
||fails
Target Milestone|--- |4.3.5
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43629
[Bug tree-optimization/43629] [4.3/4.4 Regression] Struct to register optimization fails
--- Comment #2 from rguenth at gcc dot gnu dot org 2010-04-02 11:47 --- SRA introduces a use of the uninitialized value when re-constructing the unsigned long representation. That boils down to later CCP recognizing the result as undefined and thus: Visiting statement: SR.16_25 = (unsigned int) result$A3_24(D); which is likely UNDEFINED Visiting statement: SR.17_26 = (long unsigned int) SR.16_25; which is likely UNDEFINED Visiting statement: SR.18_27 = SR.17_26 << 32; which is likely UNDEFINED Visiting statement: SR.3_34 = SR.18_27 & 0x0; which is likely UNDEFINED Visiting PHI node: SR.3_2 = PHI <12885032961(2), SR.3_34(3)> Argument #0 (2 -> 4 executable) 12885032961 Value: CONSTANT 12885032961 Argument #1 (3 -> 4 executable) SR.3_34 Value: UNDEFINED PHI node value: CONSTANT 12885032961 Lattice value changed to CONSTANT 12885032961. and we completely ignore the taken path. One issue is that Visiting statement: SR.3_34 = SR.18_27 & 0x0; which is likely UNDEFINED is not 100% true - the value is only partially undefined (only the defined pieces will be used later). But of course that's splitting hairs somewhat (but it might be the easiest fix for this bug). tree-ssa-ccp.c:likely_value needs to look at regular rhs operands for literal constants (see trunk version) but also make sure to re-set all_undefined_operands if it encounters such. -- rguenth at gcc dot gnu dot org changed: What|Removed |Added AssignedTo|unassigned at gcc dot gnu |rguenth at gcc dot gnu dot |dot org |org Status|NEW |ASSIGNED Last reconfirmed|2010-04-02 11:31:52 |2010-04-02 11:47:23 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43629
[Bug tree-optimization/43629] [4.3/4.4 Regression] Struct to register optimization fails
--- Comment #7 from rguenth at gcc dot gnu dot org 2010-04-02 16:50 --- Fixed for 4.5 sofar. -- rguenth at gcc dot gnu dot org changed: What|Removed |Added Known to fail|4.3.0 4.3.4 4.4.0 4.4.3 |4.3.0 4.3.4 4.4.0 4.4.3 |4.5.0 | Known to work|4.2.4 |4.2.4 4.5.0 Summary|[4.3/4.4/4.5 Regression]|[4.3/4.4 Regression] Struct |Struct to register |to register optimization |optimization fails |fails http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43629
[Bug tree-optimization/43629] [4.3/4.4 Regression] Struct to register optimization fails
--- Comment #8 from julien dot etienne at gmail dot com 2010-04-02 20:12 --- Thanks for your help. I will try the 4.5.0 version as soon as I can access svn. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43629
[Bug tree-optimization/43629] [4.3/4.4 Regression] Struct to register optimization fails
--- Comment #9 from mikpe at it dot uu dot se 2010-04-03 19:38 --- For 4.4 the test cases (both the original struct-using one and the later integer-only one) are fixed by backporting r145184 (PR38180 fix) and then r157944. Either of them alone fixes neither test case. Bootstrapped and regression tested on x86_64-linux so far. -- mikpe at it dot uu dot se changed: What|Removed |Added CC||mikpe at it dot uu dot se http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43629
[Bug tree-optimization/43629] [4.3/4.4 Regression] Struct to register optimization fails
--- Comment #10 from rguenth at gcc dot gnu dot org 2010-04-03 19:53 --- (In reply to comment #9) > For 4.4 the test cases (both the original struct-using one and the later > integer-only one) are fixed by backporting r145184 (PR38180 fix) and then > r157944. Either of them alone fixes neither test case. Bootstrapped and > regression tested on x86_64-linux so far. It only needs the likely_value changes backported (for 4.3 they need to be adjusted to match the pre-tuples world). I will do the backports once 4.5.0 is out of the door. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43629
[Bug tree-optimization/43629] [4.3/4.4 Regression] Struct to register optimization fails
--- Comment #11 from rguenth at gcc dot gnu dot org 2010-04-07 15:41 --- Subject: Bug 43629 Author: rguenth Date: Wed Apr 7 15:40:43 2010 New Revision: 158070 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158070 Log: 2010-04-07 Richard Guenther PR tree-optimization/43629 * tree-ssa-ccp.c (likely_value): Properly look for constant values. Reset all_undefined_operands if we have seen a constant value. * gcc.c-torture/execute/pr43629.c: New testcase. Added: branches/gcc-4_4-branch/gcc/testsuite/gcc.c-torture/execute/pr43629.c Modified: branches/gcc-4_4-branch/gcc/ChangeLog branches/gcc-4_4-branch/gcc/testsuite/ChangeLog branches/gcc-4_4-branch/gcc/tree-ssa-ccp.c -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43629
