Added inst combine transforms for single bit tests from Chris's note

if ((x & C) == 0) x |= C becomes x |= C
if ((x & C) != 0) x ^= C becomes x &= ~C
if ((x & C) == 0) x ^= C becomes x |= C
if ((x & C) != 0) x &= ~C becomes x &= ~C
if ((x & C) == 0) x &= ~C becomes nothing

Differential Revision: http://reviews.llvm.org/D3777

llvm-svn: 210006

1 files changed, 28 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 9a41e4b9406..caf9e6af7d4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -365,7 +365,15 @@ static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
 /// 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,
+///
+/// This also tries to turn
+/// --- Single bit tests:
+/// if ((x & C) == 0) x |= C	to  x |= C
+/// if ((x & C) != 0) x ^= C	to  x &= ~C
+/// if ((x & C) == 0) x ^= C	to  x |= C
+/// if ((x & C) != 0) x &= ~C	to  x &= ~C
+/// if ((x & C) == 0) x &= ~C	to  nothing
+static Value *foldSelectICmpAndOr(SelectInst &SI, Value *TrueVal,
                                   Value *FalseVal,
                                   InstCombiner::BuilderTy *Builder) {
   const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
@@ -384,6 +392,25 @@ static Value *foldSelectICmpAndOr(const SelectInst &SI, Value *TrueVal,
     return nullptr;
 
   const APInt *C2;
+  if (match(TrueVal, m_Specific(X))) {
+    // if ((X & C) != 0) X ^= C becomes X &= ~C
+    if (match(FalseVal, m_Xor(m_Specific(X), m_APInt(C2))) && C1 == C2)
+      return Builder->CreateAnd(X, ~(*C1));
+    // if ((X & C) != 0) X &= ~C becomes X &= ~C
+    if (match(FalseVal, m_And(m_Specific(X), m_APInt(C2))) && *C1 == ~(*C2))
+      return FalseVal;
+  } else if (match(FalseVal, m_Specific(X))) {
+    // if ((X & C) == 0) X ^= C becomes X |= C
+    if (match(TrueVal, m_Xor(m_Specific(X), m_APInt(C2))) && C1 == C2)
+      return Builder->CreateOr(X, *C1);
+    // if ((X & C) == 0) X &= ~C becomes nothing
+    if (match(TrueVal, m_And(m_Specific(X), m_APInt(C2))) && *C1 == ~(*C2))
+      return X;
+    // if ((X & C) == 0) X |= C becomes X |= C
+    if (match(TrueVal, m_Or(m_Specific(X), m_APInt(C2))) && C1 == C2)
+      return TrueVal;
+  }
+
   bool OrOnTrueVal = false;
   bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
   if (!OrOnFalseVal)