[clang] [Clang] Lower fp atomic compound stmts into atomicrmw (PR #216033)

[via cfe-commits]

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@@ -4105,14 +4102,21 @@ LValue ScalarExprEmitter::EmitCompoundAssignLValue(
     // the loaded integer to double, performing FP arithmetics, and truncation
     // back as a single atomic operation. Integer promotion is still
     // semantically safe.
-    bool CanEmitAtomicRMW =
+    bool CanEmitIntegerRMW =
         !AtomicValueTy->isBooleanType() && AtomicValueTy->isIntegerType() &&
         ResultTy->isIntegerType() &&
         !(AtomicValueTy->isUnsignedIntegerType() &&
           CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow)) &&
         CGF.getLangOpts().getSignedOverflowBehavior() !=
             LangOptions::SOB_Trapping;
-    if (CanEmitAtomicRMW) {
+    bool CanEmitFloatingRMW = false;
+    if (!Builder.getIsFPConstrained() && AtomicValueTy->isFloatingType() &&
+        CGF.getContext().hasSameUnqualifiedType(AtomicValueTy, ResultTy)) {
+      llvm::Type *IRTy = CGF.ConvertType(AtomicValueTy);
+      uint64_t StoreBits = CGF.CGM.getDataLayout().getTypeStoreSizeInBits(IRTy);
+      CanEmitFloatingRMW = llvm::isPowerOf2_64(StoreBits);
+    }
+    if (CanEmitIntegerRMW || CanEmitFloatingRMW) {
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Lukacma wrote:

I hope I understood your idea and applied it correctly here.  

https://github.com/llvm/llvm-project/pull/216033