InstSimplify: Eliminate fabs on known positive

llvm-svn: 291624

2 files changed, 64 insertions, 22 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 8da2f0981d0..73dcd713416 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4308,10 +4308,21 @@ static Value *SimplifyIntrinsic(Function *F, IterTy ArgBegin, IterTy ArgEnd,
     return nullptr;
 
   // Unary Ops
-  if (NumOperands == 1)
-    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(*ArgBegin))
+  if (NumOperands == 1) {
+    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(*ArgBegin)) {
       if (II->getIntrinsicID() == IID)
         return II;
+    }
+
+    switch (IID) {
+    case Intrinsic::fabs: {
+      if (SignBitMustBeZero(*ArgBegin, Q.TLI))
+        return *ArgBegin;
+    }
+    default:
+      break;
+    }
+  }
 
   return nullptr;
 }
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index d31472c0d33..b98c9629960 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2580,51 +2580,70 @@ bool llvm::CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI,
   return false;
 }
 
-bool llvm::CannotBeOrderedLessThanZero(const Value *V,
-                                       const TargetLibraryInfo *TLI,
-                                       unsigned Depth) {
-  if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
-    return !CFP->getValueAPF().isNegative() || CFP->getValueAPF().isZero();
+/// If \p SignBitOnly is true, test for a known 0 sign bit rather than a
+/// standard ordered compare. e.g. make -0.0 olt 0.0 be true because of the sign
+/// bit despite comparing equal.
+static bool cannotBeOrderedLessThanZeroImpl(const Value *V,
+                                            const TargetLibraryInfo *TLI,
+                                            bool SignBitOnly,
+                                            unsigned Depth) {
+  if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
+    return !CFP->getValueAPF().isNegative() ||
+           (!SignBitOnly && CFP->getValueAPF().isZero());
+  }
 
   if (Depth == MaxDepth)
-    return false;  // Limit search depth.
+    return false; // Limit search depth.
 
   const Operator *I = dyn_cast<Operator>(V);
-  if (!I) return false;
+  if (!I)
+    return false;
 
   switch (I->getOpcode()) {
-  default: break;
+  default:
+    break;
   // Unsigned integers are always nonnegative.
   case Instruction::UIToFP:
     return true;
   case Instruction::FMul:
     // x*x is always non-negative or a NaN.
-    if (I->getOperand(0) == I->getOperand(1))
+    if (I->getOperand(0) == I->getOperand(1) &&
+        (!SignBitOnly || cast<FPMathOperator>(I)->hasNoNaNs()))
       return true;
+
     LLVM_FALLTHROUGH;
   case Instruction::FAdd:
   case Instruction::FDiv:
   case Instruction::FRem:
-    return CannotBeOrderedLessThanZero(I->getOperand(0), TLI, Depth + 1) &&
-           CannotBeOrderedLessThanZero(I->getOperand(1), TLI, Depth + 1);
+    return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
+                                           Depth + 1) &&
+           cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly,
+                                           Depth + 1);
   case Instruction::Select:
-    return CannotBeOrderedLessThanZero(I->getOperand(1), TLI, Depth + 1) &&
-           CannotBeOrderedLessThanZero(I->getOperand(2), TLI, Depth + 1);
+    return cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly,
+                                           Depth + 1) &&
+           cannotBeOrderedLessThanZeroImpl(I->getOperand(2), TLI, SignBitOnly,
+                                           Depth + 1);
   case Instruction::FPExt:
   case Instruction::FPTrunc:
     // Widening/narrowing never change sign.
-    return CannotBeOrderedLessThanZero(I->getOperand(0), TLI, Depth + 1);
+    return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
+                                           Depth + 1);
   case Instruction::Call:
     Intrinsic::ID IID = getIntrinsicForCallSite(cast<CallInst>(I), TLI);
     switch (IID) {
     default:
       break;
     case Intrinsic::maxnum:
-      return CannotBeOrderedLessThanZero(I->getOperand(0), TLI, Depth + 1) ||
-             CannotBeOrderedLessThanZero(I->getOperand(1), TLI, Depth + 1);
+      return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
+                                             Depth + 1) ||
+             cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly,
+                                             Depth + 1);
     case Intrinsic::minnum:
-      return CannotBeOrderedLessThanZero(I->getOperand(0), TLI, Depth + 1) &&
-             CannotBeOrderedLessThanZero(I->getOperand(1), TLI, Depth + 1);
+      return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
+                                             Depth + 1) &&
+             cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly,
+                                             Depth + 1);
     case Intrinsic::exp:
     case Intrinsic::exp2:
     case Intrinsic::fabs:
@@ -2636,18 +2655,30 @@ bool llvm::CannotBeOrderedLessThanZero(const Value *V,
         if (CI->getBitWidth() <= 64 && CI->getSExtValue() % 2u == 0)
           return true;
       }
-      return CannotBeOrderedLessThanZero(I->getOperand(0), TLI, Depth + 1);
+      return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
+                                             Depth + 1);
     case Intrinsic::fma:
     case Intrinsic::fmuladd:
       // x*x+y is non-negative if y is non-negative.
       return I->getOperand(0) == I->getOperand(1) &&
-             CannotBeOrderedLessThanZero(I->getOperand(2), TLI, Depth + 1);
+             (!SignBitOnly || cast<FPMathOperator>(I)->hasNoNaNs()) &&
+             cannotBeOrderedLessThanZeroImpl(I->getOperand(2), TLI, SignBitOnly,
+                                             Depth + 1);
     }
     break;
   }
   return false;
 }
 
+bool llvm::CannotBeOrderedLessThanZero(const Value *V,
+                                       const TargetLibraryInfo *TLI) {
+  return cannotBeOrderedLessThanZeroImpl(V, TLI, false, 0);
+}
+
+bool llvm::SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI) {
+  return cannotBeOrderedLessThanZeroImpl(V, TLI, true, 0);
+}
+
 /// If the specified value can be set by repeating the same byte in memory,
 /// return the i8 value that it is represented with.  This is
 /// true for all i8 values obviously, but is also true for i32 0, i32 -1,