miscompilation by basicaa

[llvmbot]

Bugzilla Link	2057
Resolution	FIXED
Resolved on	Feb 19, 2008 00:47
Version	unspecified
OS	Linux
Attachments	testcase .ll
Reporter	LLVM Bugzilla Contributor

Extended Description

Some recent change introduced a problem with licm.

$ llvm-as testcase.ll
$ llc testcase.bc
$ gcc -o testcase testcase.s
$ ./testcase
$ opt -licm testcase.bc > badcase.bc
$ llc badcase.bc
$ gcc -o badcase badcase.s
$ ./badcase
Aborted (core dumped)

[lattner]

Looks basicaa related:

Ok:
$ llvm-as < testcase.ll.txt | opt -no-aa -licm | lli

Bad:
$ llvm-as < testcase.ll.txt | opt -no-aa -licm | opt -licm | lli

[lattner]

Looks like the recent change to mod/ref analysis did it:

$ llvm-as < testcase.ll.txt | opt -no-aa -licm | opt -licm -debug | lli
LICM: Promoting value: %tmp599 = getelementptr [3 x i32]* %tmp2, i32 0, i32 0
LICM: Promoting value: %tmp602 = getelementptr [3 x i32]* %tmp2, i32 0, i32 1
LICM: Promoting value: %tmp605 = getelementptr [3 x i32]* %tmp2, i32 0, i32 2
LICM: Promoting value: %tmp375 = getelementptr [3 x i32]* %tmp6, i32 0, i32 0
LICM: Promoting value: %tmp378 = getelementptr [3 x i32]* %tmp6, i32 0, i32 1
LICM: Promoting value: %tmp381 = getelementptr [3 x i32]* %tmp6, i32 0, i32 2

Those promotions are happening because basicaa says the memcpy calls are not mod/ref'ing the pointers:

$ llvm-as < testcase.ll.txt | opt -no-aa -licm | opt -count-aa -licm -count-aa-print-all-queries
No alias: [4B] i32* %tmp599, [4B] i32* %tmp602
No alias: [4B] i32* %tmp599, [4B] i32* %tmp605
No alias: [4B] i32* %tmp602, [4B] i32* %tmp605
NoModRef: Ptr: [4B] i32* %tmp599 <-> call void @​llvm.memcpy.i32( i8* %tmp614, i8* %tmp2608620, i32 %tmp174, i32 1 )
NoModRef: Ptr: [4B] i32* %tmp602 <-> call void @​llvm.memcpy.i32( i8* %tmp614, i8* %tmp2608620, i32 %tmp174, i32 1 )
NoModRef: Ptr: [4B] i32* %tmp605 <-> call void @​llvm.memcpy.i32( i8* %tmp614, i8* %tmp2608620, i32 %tmp174, i32 1 )
No alias: [4B] i32* %tmp375, [4B] i32* %tmp378
No alias: [4B] i32* %tmp375, [4B] i32* %tmp381
No alias: [4B] i32* %tmp378, [4B] i32* %tmp381
NoModRef: Ptr: [4B] i32* %tmp375 <-> call void @​llvm.memcpy.i32( i8* %tmp390, i8* %tmp6384396, i32 %tmp174, i32 1 )
NoModRef: Ptr: [4B] i32* %tmp378 <-> call void @​llvm.memcpy.i32( i8* %tmp390, i8* %tmp6384396, i32 %tmp174, i32 1 )
NoModRef: Ptr: [4B] i32* %tmp381 <-> call void @​llvm.memcpy.i32( i8* %tmp390, i8* %tmp6384396, i32 %tmp174, i32 1 )

===== Alias Analysis Counter Report =====
Analysis counted: Basic Alias Analysis (default AA impl)
6 Total Alias Queries Performed
6 no alias responses (100%)
0 may alias responses (0%)
0 must alias responses (0%)
Alias Analysis Counter Summary: 100%/0%/0%

6 Total Mod/Ref Queries Performed
6 no mod/ref responses (100%)
0 ref responses (0%)
0 mod responses (0%)
0 mod/ref responses (0%)
Mod/Ref Analysis Counter Summary: 100%/0%/0%/0%

[llvmbot]

Fixed with r47317.