From: Chris Lattner <sabre@nondot.org>
Date: Tue, 19 Feb 2008 06:12:18 +0000 (+0000)
Subject: fdiv/frem of undef can produce undef, because the undef operand
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=50b2ca4c73c614574a847c43ad9b87301367c59b;p=oota-llvm.git

fdiv/frem of undef can produce undef, because the undef operand
can be a SNaN.  We could be more aggressive and turn this into
unreachable, but that is less nice, and not really worth it.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47313 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 5582f511340..9957bc19c69 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2590,9 +2590,13 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
 Instruction *InstCombiner::commonDivTransforms(BinaryOperator &I) {
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
-  // undef / X -> 0
-  if (isa<UndefValue>(Op0))
+  // undef / X -> 0        for integer.
+  // undef / X -> undef    for FP (the undef could be a snan).
+  if (isa<UndefValue>(Op0)) {
+    if (Op0->getType()->isFPOrFPVector())
+      return ReplaceInstUsesWith(I, Op0);
     return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
+  }
 
   // X / undef -> undef
   if (isa<UndefValue>(Op1))
@@ -2821,13 +2825,16 @@ static Constant *GetFactor(Value *V) {
 Instruction *InstCombiner::commonRemTransforms(BinaryOperator &I) {
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
-  // 0 % X == 0, we don't need to preserve faults!
+  // 0 % X == 0 for integer, we don't need to preserve faults!
   if (Constant *LHS = dyn_cast<Constant>(Op0))
     if (LHS->isNullValue())
       return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
 
-  if (isa<UndefValue>(Op0))              // undef % X -> 0
+  if (isa<UndefValue>(Op0)) {             // undef % X -> 0
+    if (I.getType()->isFPOrFPVector())
+      return ReplaceInstUsesWith(I, Op0);  // X % undef -> undef (could be SNaN)
     return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
+  }
   if (isa<UndefValue>(Op1))
     return ReplaceInstUsesWith(I, Op1);  // X % undef -> undef