Fix "Combine bit test + conditional or into simple math"
This fixes the optimization introduced in r179748 and reverted in r179750.
While the optimization was sound, it did not properly respect differences in
bit-width.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180777 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index fa946e6..a34b73a 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -350,6 +350,67 @@
return 0;
}
+/// foldSelectICmpAndOr - We want to turn:
+/// (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
+/// into:
+/// (or (shl (and X, C1), C3), y)
+/// iff:
+/// C1 and C2 are both powers of 2
+/// where:
+/// C3 = Log(C2) - Log(C1)
+///
+/// This transform handles cases where:
+/// 1. The icmp predicate is inverted
+/// 2. The select operands are reversed
+/// 3. The magnitude of C2 and C1 are flipped
+static Value *foldSelectICmpAndOr(const SelectInst &SI, Value *TrueVal,
+ Value *FalseVal,
+ InstCombiner::BuilderTy *Builder) {
+ const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
+ if (!IC || !IC->isEquality())
+ return 0;
+
+ Value *CmpLHS = IC->getOperand(0);
+ Value *CmpRHS = IC->getOperand(1);
+
+ if (!match(CmpRHS, m_Zero()))
+ return 0;
+
+ Value *X;
+ const APInt *C1;
+ if (!match(CmpLHS, m_And(m_Value(X), m_Power2(C1))))
+ return 0;
+
+ const APInt *C2;
+ bool OrOnTrueVal = false;
+ bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
+ if (!OrOnFalseVal)
+ OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
+
+ if (!OrOnFalseVal && !OrOnTrueVal)
+ return 0;
+
+ Value *V = CmpLHS;
+ Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
+
+ unsigned C1Log = C1->logBase2();
+ unsigned C2Log = C2->logBase2();
+ if (C2Log > C1Log) {
+ V = Builder->CreateZExtOrTrunc(V, Y->getType());
+ V = Builder->CreateShl(V, C2Log - C1Log);
+ } else if (C1Log > C2Log) {
+ V = Builder->CreateLShr(V, C1Log - C2Log);
+ V = Builder->CreateZExtOrTrunc(V, Y->getType());
+ }
+
+ ICmpInst::Predicate Pred = IC->getPredicate();
+ if ((Pred == ICmpInst::ICMP_NE && OrOnFalseVal) ||
+ (Pred == ICmpInst::ICMP_EQ && OrOnTrueVal))
+ V = Builder->CreateXor(V, *C2);
+
+ return Builder->CreateOr(V, Y);
+}
+
/// visitSelectInstWithICmp - Visit a SelectInst that has an
/// ICmpInst as its first operand.
///
@@ -521,6 +582,9 @@
}
}
+ if (Value *V = foldSelectICmpAndOr(SI, TrueVal, FalseVal, Builder))
+ return ReplaceInstUsesWith(SI, V);
+
return Changed ? &SI : 0;
}