[InstSimplify] analyze (optionally casted) icmps to eliminate obviously false logic (PR27869)
By moving this transform to InstSimplify from InstCombine, we sidestep the problem/question
raised by PR27869:
https://llvm.org/bugs/show_bug.cgi?id=27869
...where InstCombine turns an icmp+zext into a shift causing us to miss the fold.
Credit to David Majnemer for a draft patch of the changes to InstructionSimplify.cpp.
Differential Revision: http://reviews.llvm.org/D21512
llvm-svn: 273200
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 25ce4db..746b740 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1492,9 +1492,8 @@
return nullptr;
}
-/// Simplify (and (icmp ...) (icmp ...)) to true when we can tell that the range
-/// of possible values cannot be satisfied.
static Value *SimplifyAndOfICmps(ICmpInst *Op0, ICmpInst *Op1) {
+ Type *ITy = Op0->getType();
ICmpInst::Predicate Pred0, Pred1;
ConstantInt *CI1, *CI2;
Value *V;
@@ -1502,6 +1501,18 @@
if (Value *X = simplifyUnsignedRangeCheck(Op0, Op1, /*IsAnd=*/true))
return X;
+ // Look for this pattern: (icmp V, C0) & (icmp V, C1)).
+ const APInt *C0, *C1;
+ if (match(Op0, m_ICmp(Pred0, m_Value(V), m_APInt(C0))) &&
+ match(Op1, m_ICmp(Pred1, m_Specific(V), m_APInt(C1)))) {
+ // Make a constant range that's the intersection of the two icmp ranges.
+ // If the intersection is empty, we know that the result is false.
+ auto Range0 = ConstantRange::makeAllowedICmpRegion(Pred0, *C0);
+ auto Range1 = ConstantRange::makeAllowedICmpRegion(Pred1, *C1);
+ if (Range0.intersectWith(Range1).isEmptySet())
+ return getFalse(ITy);
+ }
+
if (!match(Op0, m_ICmp(Pred0, m_Add(m_Value(V), m_ConstantInt(CI1)),
m_ConstantInt(CI2))))
return nullptr;
@@ -1509,8 +1520,6 @@
if (!match(Op1, m_ICmp(Pred1, m_Specific(V), m_Specific(CI1))))
return nullptr;
- Type *ITy = Op0->getType();
-
auto *AddInst = cast<BinaryOperator>(Op0->getOperand(0));
bool isNSW = AddInst->hasNoSignedWrap();
bool isNUW = AddInst->hasNoUnsignedWrap();
@@ -1608,6 +1617,24 @@
}
}
+ // The compares may be hidden behind casts. Look through those and try the
+ // same folds as above.
+ auto *Cast0 = dyn_cast<CastInst>(Op0);
+ auto *Cast1 = dyn_cast<CastInst>(Op1);
+ if (Cast0 && Cast1 && Cast0->getOpcode() == Cast1->getOpcode() &&
+ Cast0->getSrcTy() == Cast1->getSrcTy()) {
+ auto *Cmp0 = dyn_cast<ICmpInst>(Cast0->getOperand(0));
+ auto *Cmp1 = dyn_cast<ICmpInst>(Cast1->getOperand(0));
+ if (Cmp0 && Cmp1) {
+ Instruction::CastOps CastOpc = Cast0->getOpcode();
+ Type *ResultType = Cast0->getType();
+ if (auto *V = dyn_cast_or_null<Constant>(SimplifyAndOfICmps(Cmp0, Cmp1)))
+ return ConstantExpr::getCast(CastOpc, V, ResultType);
+ if (auto *V = dyn_cast_or_null<Constant>(SimplifyAndOfICmps(Cmp1, Cmp0)))
+ return ConstantExpr::getCast(CastOpc, V, ResultType);
+ }
+ }
+
// Try some generic simplifications for associative operations.
if (Value *V = SimplifyAssociativeBinOp(Instruction::And, Op0, Op1, Q,
MaxRecurse))