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, 2 insertions, 10 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 761b8332ec4..c7f662140d4 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -991,8 +991,7 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
   }
   case Instruction::BitCast: {
     Type *SrcTy = I->getOperand(0)->getType();
-    if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy() ||
-         SrcTy->isFloatingPointTy()) &&
+    if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) &&
         // TODO: For now, not handling conversions like:
         // (bitcast i64 %x to <2 x i32>)
         !I->getType()->isVectorTy()) {
@@ -1316,12 +1315,6 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
         // of bits which might be set provided by popcnt KnownOne2.
         break;
       }
-      case Intrinsic::fabs: {
-        Type *Ty = II->getType();
-        APInt SignBit = APInt::getSignBit(Ty->getScalarSizeInBits());
-        KnownZero |= APInt::getSplat(Ty->getPrimitiveSizeInBits(), SignBit);
-        break;
-      }
       case Intrinsic::x86_sse42_crc32_64_64:
         KnownZero |= APInt::getHighBitsSet(64, 32);
         break;
@@ -1381,9 +1374,8 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
   unsigned BitWidth = KnownZero.getBitWidth();
 
   assert((V->getType()->isIntOrIntVectorTy() ||
-          V->getType()->isFPOrFPVectorTy() ||
           V->getType()->getScalarType()->isPointerTy()) &&
-         "Not integer, floating point, or pointer type!");
+         "Not integer or pointer type!");
   assert((Q.DL.getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) &&
          (!V->getType()->isIntOrIntVectorTy() ||
           V->getType()->getScalarSizeInBits() == BitWidth) &&