From: Reid Spencer <rspencer@reidspencer.com>
Date: Fri, 23 Mar 2007 05:33:23 +0000 (+0000)
Subject: Fix constant fold of div by zero and rem by zero to match IEEE 754
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=b8f1c1657f1b63f92957c5b1c5a4e26e4945c34d;p=oota-llvm.git

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 05a75883a1a..d7e51956e4d 100644
--- 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)) {