[PATCH] D65150: [InstSimplify] Drop leftover "division-by-zero guard" around `@llvm.umul.with.overflow` overflow bit
Roman Lebedev via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Jul 23 07:32:52 PDT 2019
lebedev.ri created this revision.
lebedev.ri added reviewers: nikic, spatel, xbolva00.
lebedev.ri added a project: LLVM.
Herald added a subscriber: hiraditya.
Now that with D65143 <https://reviews.llvm.org/D65143>/D65144 <https://reviews.llvm.org/D65144> we've produce `@llvm.umul.with.overflow`,
and with D65147 <https://reviews.llvm.org/D65147>+D65148 <https://reviews.llvm.org/D65148> we've flattened the CFG, we now can see that
the guard may have been there to prevent division by zero is redundant.
We can simply drop it:
----------------------------------------
Name: no overflow and not zero
%iszero = icmp ne i4 %y, 0
%umul = umul_overflow i4 %x, %y
%umul.ov = extractvalue {i4, i1} %umul, 1
%retval.0 = and i1 %iszero, %umul.ov
ret i1 %retval.0
=>
%iszero = icmp ne i4 %y, 0
%umul = umul_overflow i4 %x, %y
%umul.ov = extractvalue {i4, i1} %umul, 1
%retval.0 = and i1 %iszero, %umul.ov
ret %umul.ov
Done: 1
Optimization is correct!
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D65150
Files:
llvm/lib/Analysis/InstructionSimplify.cpp
llvm/test/Transforms/InstSimplify/div-by-0-guard-before-smul_ov.ll
llvm/test/Transforms/InstSimplify/div-by-0-guard-before-umul_ov.ll
llvm/test/Transforms/PhaseOrdering/unsigned-multiply-overflow-check.ll
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