https://llvm.org/bugs/show_bug.cgi?id=28443
Bug ID: 28443
Summary: integer truncation error in
areStridedAccessesIndependent
Product: new-bugs
Version: 3.8
Hardware: PC
OS: FreeBSD
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: cperc...@freebsd.org
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Created attachment 16701
--> https://llvm.org/bugs/attachment.cgi?id=16701&action=edit
Test case; crashes clang38 -O2
The attached reduced test case crashes clang38 -c -O2 on my FreeBSD/amd64
system:
Assertion failed: (Distance > 0 && "The distance must be non-zero"), function
areStridedAccessesIndependent, file
/wrkdirs/usr/ports/devel/llvm38/work/llvm-3.8.0.src/lib/Analysis/LoopAccessAnalysis.cpp,
line 1004.
This is because the function areStridedAccessIndependent takes "unsigned"
values
static bool areStridedAccessesIndependent(unsigned Distance, unsigned Stride,
unsigned TypeByteSize)
where it should be taking target size_t values: I am compiling for a 64-bit
platform, and the distance between memory accesses is 2^32 bytes, but the
"unsigned" type is a 32-bit integer so 2^32 gets truncated to 0.
In addition to causing a crash when the distance between memory accesses is a
multiple of 2^32 bytes, this bug could theoretically cause incorrect code
generation, e.g., if the distance is 2^32+2 bytes and the stride length is
2^31+1; using 32-bit integers it appears that the distance is not a multiple of
the stride length, and invalid optimizations may occur.
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