https://llvm.org/bugs/show_bug.cgi?id=31439
Bug ID: 31439
Summary: LLVM consider GEP(a + i - 1) could not be zero
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Global Analyses
Assignee: unassignedb...@nondot.org
Reporter: evstu...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
char *foo() {
return 0;
}
int main(int argc, char *argv[]) {
if(foo() + argc - 1)
return 1;
return 0;
}
clang test.c -O0
./a.out; echo $?
0
clang test.c -O3
./a.out; echo $?
1
The transformation that leads to this is Early CSE:
ValueTracking.cpp:
isGEPKnownNonNull consider GEP is not null if one of its operands is constant.
That way LLVMoptimize "if(foo() + argc - 1)" to always true.
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