[llvm] r177279 - The optimization a + (-0.0f) -> a was being misapplied to a + (+0.0f) in the vector case (because

[David Tweed]

Author: davidtweed
Date: Mon Mar 18 06:54:44 2013
New Revision: 177279

URL: http://llvm.org/viewvc/llvm-project?rev=177279&view=rev
Log:
 The optimization a + (-0.0f) -> a was being misapplied to a + (+0.0f) in the vector case (because
we weren't differntiating floating-point zeroinitializers from other zero-initializers)
which was causing problems for code relying upon a + (+0.0f) to, eg, flush denormals to
0. Make the scalar and vector cases have the same behaviour.


Modified:
    llvm/trunk/lib/IR/Constants.cpp

Modified: llvm/trunk/lib/IR/Constants.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Constants.cpp?rev=177279&r1=177278&r2=177279&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Constants.cpp (original)
+++ llvm/trunk/lib/IR/Constants.cpp Mon Mar 18 06:54:44 2013
@@ -47,6 +47,19 @@ bool Constant::isNegativeZeroValue() con
   if (const ConstantFP *CFP = dyn_cast<ConstantFP>(this))
     return CFP->isZero() && CFP->isNegative();
 
+  // Equivalent for a vector of -0.0's.
+  if (const ConstantDataVector *CV = dyn_cast<ConstantDataVector>(this))
+    if (ConstantFP *SplatCFP = dyn_cast_or_null<ConstantFP>(CV->getSplatValue()))
+      if (SplatCFP && SplatCFP->isZero() && SplatCFP->isNegative())
+        return true;
+
+  // However, vectors of zeroes which are floating point represent +0.0's.
+  if (const ConstantAggregateZero *CAZ = dyn_cast<ConstantAggregateZero>(this))
+    if (const VectorType *VT = dyn_cast<VectorType>(CAZ->getType()))
+      if (VT->getElementType()->isFloatingPointTy())
+        // As it's a CAZ, we know it's the zero bit-pattern (ie, +0.0) in each element.
+        return false;
+
   // Otherwise, just use +0.0.
   return isNullValue();
 }