pull a bunch of logic out of instcombine into instsimplify for compare

simplification, this handles the foldable fcmp x,x cases among many others.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86627 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 93 insertions, 5 deletions

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 0369ab3..367a7d4 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -31,6 +31,10 @@ Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
   return 0;
 }
 
+static const Type *GetCompareTy(Value *Op) {
+  return CmpInst::makeCmpResultType(Op->getType());
+}
+
 
 /// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
 /// fold the result.  If not, this returns null.
@@ -43,13 +47,59 @@ Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     if (Constant *CRHS = dyn_cast<Constant>(RHS))
       return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
   
-  // If this is an integer compare and the LHS and RHS are the same, fold it.
+  // ITy - This is the return type of the compare we're considering.
+  const Type *ITy = GetCompareTy(LHS);
+  
+  // icmp X, X -> true/false
   if (LHS == RHS)
-    if (ICmpInst::isTrueWhenEqual(Pred))
-      return ConstantInt::getTrue(LHS->getContext());
-    else
-      return ConstantInt::getFalse(LHS->getContext());
+    return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
+
+  // If we have a constant, make sure it is on the RHS.
+  if (isa<Constant>(LHS)) {
+    std::swap(LHS, RHS);
+    Pred = CmpInst::getSwappedPredicate(Pred);
+  }
 
+  if (isa<UndefValue>(RHS))                  // X icmp undef -> undef
+    return UndefValue::get(ITy);
+  
+  // icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
+  // addresses never equal each other!  We already know that Op0 != Op1.
+  if ((isa<GlobalValue>(LHS) || isa<AllocaInst>(LHS) || 
+       isa<ConstantPointerNull>(LHS)) &&
+      (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) || 
+       isa<ConstantPointerNull>(RHS)))
+    return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
+  
+  // See if we are doing a comparison with a constant.
+  if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
+    // If we have an icmp le or icmp ge instruction, turn it into the
+    // appropriate icmp lt or icmp gt instruction.  This allows us to rely on
+    // them being folded in the code below.
+    switch (Pred) {
+    default: break;
+    case ICmpInst::ICMP_ULE:
+      if (CI->isMaxValue(false))                 // A <=u MAX -> TRUE
+        return ConstantInt::getTrue(CI->getContext());
+      break;
+    case ICmpInst::ICMP_SLE:
+      if (CI->isMaxValue(true))                  // A <=s MAX -> TRUE
+        return ConstantInt::getTrue(CI->getContext());
+      break;
+    case ICmpInst::ICMP_UGE:
+      if (CI->isMinValue(false))                 // A >=u MIN -> TRUE
+        return ConstantInt::getTrue(CI->getContext());
+      break;
+    case ICmpInst::ICMP_SGE:
+      if (CI->isMinValue(true))                  // A >=s MIN -> TRUE
+        return ConstantInt::getTrue(CI->getContext());
+      break;
+    }
+    
+    
+  }
+  
+  
   return 0;
 }
 
@@ -64,6 +114,44 @@ Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     if (Constant *CRHS = dyn_cast<Constant>(RHS))
       return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
   
+  // Fold trivial predicates.
+  if (Pred == FCmpInst::FCMP_FALSE)
+    return ConstantInt::get(GetCompareTy(LHS), 0);
+  if (Pred == FCmpInst::FCMP_TRUE)
+    return ConstantInt::get(GetCompareTy(LHS), 1);
+
+  // If we have a constant, make sure it is on the RHS.
+  if (isa<Constant>(LHS)) {
+    std::swap(LHS, RHS);
+    Pred = CmpInst::getSwappedPredicate(Pred);
+  }
+  
+  if (isa<UndefValue>(RHS))                  // fcmp pred X, undef -> undef
+    return UndefValue::get(GetCompareTy(LHS));
+
+  // fcmp x,x -> true/false.  Not all compares are foldable.
+  if (LHS == RHS) {
+    if (CmpInst::isTrueWhenEqual(Pred))
+      return ConstantInt::get(GetCompareTy(LHS), 1);
+    if (CmpInst::isFalseWhenEqual(Pred))
+      return ConstantInt::get(GetCompareTy(LHS), 0);
+  }
+  
+  // Handle fcmp with constant RHS
+  if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
+    // If the constant is a nan, see if we can fold the comparison based on it.
+    if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
+      if (CFP->getValueAPF().isNaN()) {
+        if (FCmpInst::isOrdered(Pred))   // True "if ordered and foo"
+          return ConstantInt::getFalse(CFP->getContext());
+        assert(FCmpInst::isUnordered(Pred) &&
+               "Comparison must be either ordered or unordered!");
+        // True if unordered.
+        return ConstantInt::getTrue(CFP->getContext());
+      }
+    }
+  }
+  
   return 0;
 }