[InstSimplify] use ConstantRange to simplify more and-of-icmps

We can simplify (and (icmp X, C1), (icmp X, C2)) to one of the icmps in many cases. 
I had to check some of these with Alive to prove to myself it's right, but everything 
seems to check out. Eg, the code in instcombine was completely ignoring predicates with 
mismatched signedness.

Handling or-of-icmps would be a follow-up step.

Differential Revision: https://reviews.llvm.org/D32143

llvm-svn: 301260

2 files changed, 9 insertions, 42 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 0f60f1ba8a9..be9beebe189 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1575,6 +1575,7 @@ static Value *SimplifyAndOfICmps(ICmpInst *Op0, ICmpInst *Op1) {
   if (Value *X = simplifyAndOfICmpsWithSameOperands(Op0, Op1))
     return X;
 
+  // FIXME: This should be shared with or-of-icmps.
   // Look for this pattern: (icmp V, C0) & (icmp V, C1)).
   Type *ITy = Op0->getType();
   ICmpInst::Predicate Pred0, Pred1;
@@ -1584,10 +1585,16 @@ static Value *SimplifyAndOfICmps(ICmpInst *Op0, ICmpInst *Op1) {
       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);
+    auto Range0 = ConstantRange::makeExactICmpRegion(Pred0, *C0);
+    auto Range1 = ConstantRange::makeExactICmpRegion(Pred1, *C1);
     if (Range0.intersectWith(Range1).isEmptySet())
       return getFalse(ITy);
+
+    // If a range is a superset of the other, the smaller set is all we need.
+    if (Range0.contains(Range1))
+      return Op1;
+    if (Range1.contains(Range0))
+      return Op0;
   }
 
   // (icmp (add V, C0), C1) & (icmp V, C0)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 9baaeadb8df..292c8852a53 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -906,15 +906,6 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
   switch (PredL) {
   default:
     llvm_unreachable("Unknown integer condition code!");
-  case ICmpInst::ICMP_EQ:
-    switch (PredR) {
-    default:
-      llvm_unreachable("Unknown integer condition code!");
-    case ICmpInst::ICMP_NE:  // (X == 13 & X != 15) -> X == 13
-    case ICmpInst::ICMP_ULT: // (X == 13 & X <  15) -> X == 13
-    case ICmpInst::ICMP_SLT: // (X == 13 & X <  15) -> X == 13
-      return LHS;
-    }
   case ICmpInst::ICMP_NE:
     switch (PredR) {
     default:
@@ -930,43 +921,15 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
       if (LHSC == SubOne(RHSC)) // (X != 13 & X s< 14) -> X < 13
         return Builder->CreateICmpSLT(LHS0, LHSC);
       break;                 // (X != 13 & X s< 15) -> no change
-    case ICmpInst::ICMP_EQ:  // (X != 13 & X == 15) -> X == 15
-    case ICmpInst::ICMP_UGT: // (X != 13 & X u> 15) -> X u> 15
-    case ICmpInst::ICMP_SGT: // (X != 13 & X s> 15) -> X s> 15
-      return RHS;
     case ICmpInst::ICMP_NE:
       // Potential folds for this case should already be handled.
       break;
     }
     break;
-  case ICmpInst::ICMP_ULT:
-    switch (PredR) {
-    default:
-      llvm_unreachable("Unknown integer condition code!");
-    case ICmpInst::ICMP_EQ:  // (X u< 13 & X == 15) -> false
-    case ICmpInst::ICMP_UGT: // (X u< 13 & X u> 15) -> false
-      return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0);
-    case ICmpInst::ICMP_NE:  // (X u< 13 & X != 15) -> X u< 13
-    case ICmpInst::ICMP_ULT: // (X u< 13 & X u< 15) -> X u< 13
-      return LHS;
-    }
-    break;
-  case ICmpInst::ICMP_SLT:
-    switch (PredR) {
-    default:
-      llvm_unreachable("Unknown integer condition code!");
-    case ICmpInst::ICMP_NE:  // (X s< 13 & X != 15) -> X < 13
-    case ICmpInst::ICMP_SLT: // (X s< 13 & X s< 15) -> X < 13
-      return LHS;
-    }
-    break;
   case ICmpInst::ICMP_UGT:
     switch (PredR) {
     default:
       llvm_unreachable("Unknown integer condition code!");
-    case ICmpInst::ICMP_EQ:  // (X u> 13 & X == 15) -> X == 15
-    case ICmpInst::ICMP_UGT: // (X u> 13 & X u> 15) -> X u> 15
-      return RHS;
     case ICmpInst::ICMP_NE:
       if (RHSC == AddOne(LHSC)) // (X u> 13 & X != 14) -> X u> 14
         return Builder->CreateICmp(PredL, LHS0, RHSC);
@@ -980,9 +943,6 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
     switch (PredR) {
     default:
       llvm_unreachable("Unknown integer condition code!");
-    case ICmpInst::ICMP_EQ:  // (X s> 13 & X == 15) -> X == 15
-    case ICmpInst::ICMP_SGT: // (X s> 13 & X s> 15) -> X s> 15
-      return RHS;
     case ICmpInst::ICMP_NE:
       if (RHSC == AddOne(LHSC)) // (X s> 13 & X != 14) -> X s> 14
         return Builder->CreateICmp(PredL, LHS0, RHSC);