transform obscured FP sign bit ops into a fabs/fneg using TLI hook

This is effectively a revert of:
http://reviews.llvm.org/rL249702 - [InstCombine] transform masking off of an FP sign bit into a fabs() intrinsic call (PR24886)
and:
http://reviews.llvm.org/rL249701 - [ValueTracking] teach computeKnownBits that a fabs() clears sign bits
and a reimplementation as a DAG combine for targets that have IEEE754-compliant fabs/fneg instructions.

This is intended to resolve the objections raised on the dev list:
http://lists.llvm.org/pipermail/llvm-dev/2016-April/098154.html
and:
https://llvm.org/bugs/show_bug.cgi?id=24886#c4

In the interest of patch minimalism, I've only partly enabled AArch64. PowerPC, MIPS, x86 and others can enable later.

Differential Revision: http://reviews.llvm.org/D19391

llvm-svn: 271573

1 files changed, 0 insertions, 18 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index c40d28f44aa..4d653e5d611 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1594,24 +1594,6 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
   if (Instruction *CastedAnd = foldCastedBitwiseLogic(I))
     return CastedAnd;
 
-  if (CastInst *Op0C = dyn_cast<CastInst>(Op0)) {
-    Value *Op0COp = Op0C->getOperand(0);
-    Type *SrcTy = Op0COp->getType();
-
-    // If we are masking off the sign bit of a floating-point value, convert
-    // this to the canonical fabs intrinsic call and cast back to integer.
-    // The backend should know how to optimize fabs().
-    // TODO: This transform should also apply to vectors.
-    ConstantInt *CI;
-    if (isa<BitCastInst>(Op0C) && SrcTy->isFloatingPointTy() &&
-        match(Op1, m_ConstantInt(CI)) && CI->isMaxValue(true)) {
-      Module *M = I.getModule();
-      Function *Fabs = Intrinsic::getDeclaration(M, Intrinsic::fabs, SrcTy);
-      Value *Call = Builder->CreateCall(Fabs, Op0COp, "fabs");
-      return CastInst::CreateBitOrPointerCast(Call, I.getType());
-    }
-  }
-
   if (Instruction *Select = foldBoolSextMaskToSelect(I))
     return Select;