InstCombine: Make switch folding with equality compares more aggressive by trying instsimplify on the arm where we know the compared value.
Stuff like "x == y ? y : x&y" now folds into "x&y".
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132185 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 75a0b43..2a451ce 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -278,6 +278,49 @@
return 0;
}
+/// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
+/// replaced with RepOp.
+static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
+ const TargetData *TD) {
+ // Trivial replacement.
+ if (V == Op)
+ return RepOp;
+
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (!I)
+ return 0;
+
+ // If this is a binary operator, try to simplify it with the replaced op.
+ if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
+ if (B->getOperand(0) == Op)
+ return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD);
+ if (B->getOperand(1) == Op)
+ return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD);
+ }
+
+ // If all operands are constant after substituting Op for RepOp then we can
+ // constant fold the instruction.
+ if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
+ // Build a list of all constant operands.
+ SmallVector<Constant*, 8> ConstOps;
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
+ if (I->getOperand(i) == Op)
+ ConstOps.push_back(CRepOp);
+ else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
+ ConstOps.push_back(COp);
+ else
+ break;
+ }
+
+ // All operands were constants, fold it.
+ if (ConstOps.size() == I->getNumOperands())
+ return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
+ ConstOps.data(), ConstOps.size(), TD);
+ }
+
+ return 0;
+}
+
/// visitSelectInstWithICmp - Visit a SelectInst that has an
/// ICmpInst as its first operand.
///
@@ -416,25 +459,21 @@
}
}
- if (CmpLHS == TrueVal && CmpRHS == FalseVal) {
- // Transform (X == Y) ? X : Y -> Y
- if (Pred == ICmpInst::ICMP_EQ)
+ // If we have an equality comparison then we know the value in one of the
+ // arms of the select. See if substituting this value into the arm and
+ // simplifying the result yields the same value as the other arm.
+ if (Pred == ICmpInst::ICMP_EQ) {
+ if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD) == TrueVal ||
+ SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD) == TrueVal)
return ReplaceInstUsesWith(SI, FalseVal);
- // Transform (X != Y) ? X : Y -> X
- if (Pred == ICmpInst::ICMP_NE)
+ } else if (Pred == ICmpInst::ICMP_NE) {
+ if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD) == FalseVal ||
+ SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD) == FalseVal)
return ReplaceInstUsesWith(SI, TrueVal);
- /// NOTE: if we wanted to, this is where to detect integer MIN/MAX
-
- } else if (CmpLHS == FalseVal && CmpRHS == TrueVal) {
- // Transform (X == Y) ? Y : X -> X
- if (Pred == ICmpInst::ICMP_EQ)
- return ReplaceInstUsesWith(SI, FalseVal);
- // Transform (X != Y) ? Y : X -> Y
- if (Pred == ICmpInst::ICMP_NE)
- return ReplaceInstUsesWith(SI, TrueVal);
- /// NOTE: if we wanted to, this is where to detect integer MIN/MAX
}
+ // NOTE: if we wanted to, this is where to detect integer MIN/MAX
+
if (isa<Constant>(CmpRHS)) {
if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
// Transform (X == C) ? X : Y -> (X == C) ? C : Y