[InstCombine] Extend "idempotent" atomicrmw optimizations to floating point

[android-x86/external-llvm.git] / lib / Transforms / InstCombine / InstCombineAtomicRMW.cpp

diff --git a/lib/Transforms/InstCombine/InstCombineAtomicRMW.cpp b/lib/Transforms/InstCombine/InstCombineAtomicRMW.cpp
index b857741..d3a7d32 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineAtomicRMW.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAtomicRMW.cpp
@@ -21,9 +21,18 @@ namespace {
 /// TODO: Common w/ the version in AtomicExpandPass, and change the term used.
 /// Idemptotent is confusing in this context.
 bool isIdempotentRMW(AtomicRMWInst& RMWI) {
+  if (auto CF = dyn_cast<ConstantFP>(RMWI.getValOperand()))
+    switch(RMWI.getOperation()) {
+    case AtomicRMWInst::FAdd: // -0.0
+      return CF->isZero() && CF->isNegative();
+    case AtomicRMWInst::FSub: // +0.0
+      return CF->isZero() && !CF->isNegative();
+    default:
+      return false;
+    };
+  
   auto C = dyn_cast<ConstantInt>(RMWI.getValOperand());
   if(!C)
-    // TODO: Handle fadd, fsub?
     return false;
 
   switch(RMWI.getOperation()) {
@@ -116,12 +125,18 @@ Instruction *InstCombiner::visitAtomicRMWInst(AtomicRMWInst &RMWI) {
 
   // We chose to canonicalize all idempotent operations to an single
   // operation code and constant.  This makes it easier for the rest of the
-  // optimizer to match easily.  The choice of or w/zero is arbitrary.
+  // optimizer to match easily.  The choices of or w/0 and fadd w/-0.0 are
+  // arbitrary. 
   if (RMWI.getType()->isIntegerTy() &&
       RMWI.getOperation() != AtomicRMWInst::Or) {
     RMWI.setOperation(AtomicRMWInst::Or);
     RMWI.setOperand(1, ConstantInt::get(RMWI.getType(), 0));
     return &RMWI;
+  } else if (RMWI.getType()->isFloatingPointTy() &&
+             RMWI.getOperation() != AtomicRMWInst::FAdd) {
+    RMWI.setOperation(AtomicRMWInst::FAdd);
+    RMWI.setOperand(1, ConstantFP::getNegativeZero(RMWI.getType()));
+    return &RMWI;
   }
 
   // Check if the required ordering is compatible with an atomic load.