InstCombine: add more transforms

C1-X <u C2 -> (X|(C2-1)) == C1
C1-X >u C2 -> (X|C2) == C1
X-C1 <u C2 -> (X & -C2) == C1
X-C1 >u C2 -> (X & ~C2) == C1


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185909 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 42 insertions, 0 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index f4734461a6..d843842cb3 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1512,6 +1512,30 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
         return R;
     break;
 
+  case Instruction::Sub: {
+    ConstantInt *LHSC = dyn_cast<ConstantInt>(LHSI->getOperand(0));
+    if (!LHSC) break;
+    const APInt &LHSV = LHSC->getValue();
+
+    // C1-X <u C2 -> (X|(C2-1)) == C1
+    //   iff C1 & (C2-1) == C2-1
+    //       C2 is a power of 2
+    if (ICI.getPredicate() == ICmpInst::ICMP_ULT && LHSI->hasOneUse() &&
+        RHSV.isPowerOf2() && (LHSV & (RHSV - 1)) == (RHSV - 1))
+      return new ICmpInst(ICmpInst::ICMP_EQ,
+                          Builder->CreateOr(LHSI->getOperand(1), RHSV - 1),
+                          LHSC);
+
+    // C1-X >u C2 -> (X|C2) == C1
+    //   iff C1 & C2 == C2
+    //       C2+1 is a power of 2
+    if (ICI.getPredicate() == ICmpInst::ICMP_UGT && LHSI->hasOneUse() &&
+        (RHSV + 1).isPowerOf2() && (LHSV & RHSV) == RHSV)
+      return new ICmpInst(ICmpInst::ICMP_NE,
+                          Builder->CreateOr(LHSI->getOperand(1), RHSV), LHSC);
+    break;
+  }
+
   case Instruction::Add:
     // Fold: icmp pred (add X, C1), C2
     if (!ICI.isEquality()) {
@@ -1708,6 +1732,24 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
       default:
         break;
       }
+
+      // X-C1 <u C2 -> (X & -C2) == C1
+      //   iff C1 & (C2-1) == 0
+      //       C2 is a power of 2
+      if (ICI.getPredicate() == ICmpInst::ICMP_ULT && LHSI->hasOneUse() &&
+          RHSV.isPowerOf2() && (LHSV & (RHSV - 1)) == 0)
+        return new ICmpInst(ICmpInst::ICMP_EQ,
+                            Builder->CreateAnd(LHSI->getOperand(0), -RHSV),
+                            ConstantExpr::getNeg(LHSC));
+
+      // X-C1 >u C2 -> (X & ~C2) == C1
+      //   iff C1 & C2 == 0
+      //       C2+1 is a power of 2
+      if (ICI.getPredicate() == ICmpInst::ICMP_UGT && LHSI->hasOneUse() &&
+          (RHSV + 1).isPowerOf2() && (LHSV & RHSV) == 0)
+        return new ICmpInst(ICmpInst::ICMP_NE,
+                            Builder->CreateAnd(LHSI->getOperand(0), ~RHSV),
+                            ConstantExpr::getNeg(LHSC));
     }
   }
   return 0;