The expression icmp eq (select (icmp eq x, 0), 1, x), 0 folds to false.
Spotted by my super-optimizer in 186.crafty and 450.soplex. We really
need a proper infrastructure for handling generalizations of this kind
of thing (which occur a lot), however this case is so simple that I decided
to go ahead and implement it directly.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143214 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 6bef0ae..83881de 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -416,39 +416,55 @@
}
assert(isa<SelectInst>(LHS) && "Not comparing with a select instruction!");
SelectInst *SI = cast<SelectInst>(LHS);
+ Value *Cond = SI->getCondition();
+ Value *TV = SI->getTrueValue();
+ Value *FV = SI->getFalseValue();
// Now that we have "cmp select(Cond, TV, FV), RHS", analyse it.
// Does "cmp TV, RHS" simplify?
- if (Value *TCmp = SimplifyCmpInst(Pred, SI->getTrueValue(), RHS, TD, DT,
- MaxRecurse)) {
- // It does! Does "cmp FV, RHS" simplify?
- if (Value *FCmp = SimplifyCmpInst(Pred, SI->getFalseValue(), RHS, TD, DT,
- MaxRecurse)) {
- // It does! If they simplified to the same value, then use it as the
- // result of the original comparison.
- if (TCmp == FCmp)
- return TCmp;
- Value *Cond = SI->getCondition();
- // If the false value simplified to false, then the result of the compare
- // is equal to "Cond && TCmp". This also catches the case when the false
- // value simplified to false and the true value to true, returning "Cond".
- if (match(FCmp, m_Zero()))
- if (Value *V = SimplifyAndInst(Cond, TCmp, TD, DT, MaxRecurse))
- return V;
- // If the true value simplified to true, then the result of the compare
- // is equal to "Cond || FCmp".
- if (match(TCmp, m_One()))
- if (Value *V = SimplifyOrInst(Cond, FCmp, TD, DT, MaxRecurse))
- return V;
- // Finally, if the false value simplified to true and the true value to
- // false, then the result of the compare is equal to "!Cond".
- if (match(FCmp, m_One()) && match(TCmp, m_Zero()))
- if (Value *V =
- SimplifyXorInst(Cond, Constant::getAllOnesValue(Cond->getType()),
- TD, DT, MaxRecurse))
- return V;
- }
+ Value *TCmp = SimplifyCmpInst(Pred, TV, RHS, TD, DT, MaxRecurse);
+ if (!TCmp) {
+ // It didn't simplify. However if "cmp TV, RHS" is equal to the select
+ // condition itself then we can replace it with 'true'.
+ if (match(Cond, m_ICmp(Pred, m_Specific(TV), m_Specific(RHS))))
+ TCmp = getTrue(Cond->getType());
}
+ if (!TCmp)
+ return 0;
+
+ // Does "cmp FV, RHS" simplify?
+ Value *FCmp = SimplifyCmpInst(Pred, FV, RHS, TD, DT, MaxRecurse);
+ if (!FCmp) {
+ // It didn't simplify. However if "cmp FV, RHS" is equal to the select
+ // condition itself then we can replace it with 'false'.
+ if (match(Cond, m_ICmp(Pred, m_Specific(FV), m_Specific(RHS))))
+ FCmp = getFalse(Cond->getType());
+ }
+ if (!FCmp)
+ return 0;
+
+ // If both sides simplified to the same value, then use it as the result of
+ // the original comparison.
+ if (TCmp == FCmp)
+ return TCmp;
+ // If the false value simplified to false, then the result of the compare
+ // is equal to "Cond && TCmp". This also catches the case when the false
+ // value simplified to false and the true value to true, returning "Cond".
+ if (match(FCmp, m_Zero()))
+ if (Value *V = SimplifyAndInst(Cond, TCmp, TD, DT, MaxRecurse))
+ return V;
+ // If the true value simplified to true, then the result of the compare
+ // is equal to "Cond || FCmp".
+ if (match(TCmp, m_One()))
+ if (Value *V = SimplifyOrInst(Cond, FCmp, TD, DT, MaxRecurse))
+ return V;
+ // Finally, if the false value simplified to true and the true value to
+ // false, then the result of the compare is equal to "!Cond".
+ if (match(FCmp, m_One()) && match(TCmp, m_Zero()))
+ if (Value *V =
+ SimplifyXorInst(Cond, Constant::getAllOnesValue(Cond->getType()),
+ TD, DT, MaxRecurse))
+ return V;
return 0;
}