Fix constant fold of div by zero and rem by zero to match IEEE 754

requirements. We must return NaN in some cases and correctly signed
infinity in other cases. Passes CFP2006 (not that that says much).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35277 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp
index 05a75883a1a30e9a7a76cdf89c22a93ed2f7ceb3..d7e51956e4d274031f77253b75037d5c03745f69 100644 (file)
--- a/lib/VMCore/ConstantFold.cpp
+++ b/lib/VMCore/ConstantFold.cpp
@@ -651,17 +651,27 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
       case Instruction::Mul:     
         return ConstantFP::get(CFP1->getType(), C1Val * C2Val);
       case Instruction::FDiv:
-        if (CFP2->isExactlyValue(0.0)) 
-          return ConstantFP::get(CFP1->getType(),
-                                 std::numeric_limits<double>::infinity());
-        if (CFP2->isExactlyValue(-0.0))
-          return ConstantFP::get(CFP1->getType(),
-                                 -std::numeric_limits<double>::infinity());
+        if (CFP2->isExactlyValue(0.0) || CFP2->isExactlyValue(-0.0))
+          if (CFP1->isExactlyValue(0.0) || CFP1->isExactlyValue(-0.0))
+            // IEEE 754, Section 7.1, #4
+            return ConstantFP::get(CFP1->getType(),
+                                   std::numeric_limits<double>::quiet_NaN());
+          else if (CFP2->isExactlyValue(-0.0) || C1Val < 0.0)
+            // IEEE 754, Section 7.2, negative infinity case
+            return ConstantFP::get(CFP1->getType(),
+                                   -std::numeric_limits<double>::infinity());
+          else
+            // IEEE 754, Section 7.2, positive infinity case
+            return ConstantFP::get(CFP1->getType(),
+                                   std::numeric_limits<double>::infinity());
         return ConstantFP::get(CFP1->getType(), C1Val / C2Val);
       case Instruction::FRem:
-        if (CFP2->isNullValue()) 
-          return 0;
+        if (CFP2->isExactlyValue(0.0) || CFP2->isExactlyValue(-0.0))
+          // IEEE 754, Section 7.1, #5
+          return ConstantFP::get(CFP1->getType(), 
+                                 std::numeric_limits<double>::quiet_NaN());
         return ConstantFP::get(CFP1->getType(), std::fmod(C1Val, C2Val));
+
       }
     }
   } else if (const ConstantVector *CP1 = dyn_cast<ConstantVector>(C1)) {