https://llvm.org/bugs/show_bug.cgi?id=26862
Bug ID: 26862
Summary: InstructionSimplify broadens undef when simplifying
fdiv
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Global Analyses
Assignee: unassignedb...@nondot.org
Reporter: dav...@cs.rutgers.edu
CC: llvm-bugs@lists.llvm.org,
santosh.nagaraka...@gmail.com
Classification: Unclassified
These optimizations in SimplifyFDivInst, from
lib/Analysis/InstructionSimplify.cpp, potentially introduce new behavior.
// undef / X -> undef (the undef could be a snan).
if (match(Op0, m_Undef()))
return Op0;
// X / undef -> undef
if (match(Op1, m_Undef()))
return Op1;
In the first optimization, for any value of X, there will be some floating
point values that undef/X cannot produce. For example, if X is 0, the original
code can only evaluate to Infinity, -Infinity, or NaN, but the transformed code
may produce any value.
The second optimization is similar. For example, if X is 0, x/undef is either
0, -0, or NaN.
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