[OpenMP][Flang] Fix atomic size for complex types

Fixes #165184

In OMPIRBuilder::createAtomicRead() and createAtomicWrite(), the size
parameter for __atomic_load/__atomic_store was incorrectly computed
from the pointer type instead of the pointee (element) type.

On 64-bit systems, this resulted in only 8 bytes being transferred
regardless of the actual struct size.

Changed both functions to use XElemTy (element type) instead of the
pointer type when computing LoadSize. This ensures the full struct
is transferred.

Author: Krish Gupta

flang/test/Lower/OpenMP/atomic-read-complex.f90

@@ -0,0 +1,34 @@
+! Test lowering of atomic read to LLVM IR for complex types.
+! This is a regression test for issue #165184.
+
+! RUN: %flang_fc1 -emit-llvm -fopenmp -o - %s | FileCheck %s
+
+! Test that atomic read operations with complex types emit the correct
+! size parameter to __atomic_load:
+! - complex(4) (8 bytes total): should call __atomic_load(i64 8, ...)
+! - complex(8) (16 bytes total): should call __atomic_load(i64 16, ...)
+
+program atomic_read_complex
+  implicit none
+
+  ! Test complex(4) - single precision (8 bytes)
+  complex(4) :: c41, c42
+  ! Test complex(8) - double precision (16 bytes)
+  complex(8) :: c81, c82
+  
+  c42 = (1.0_4, 1.0_4)
+  c82 = (1.0_8, 1.0_8)
+
+  ! CHECK-LABEL: define {{.*}} @_QQmain
+
+  ! Single precision complex: 8 bytes
+  ! CHECK: call void @__atomic_load(i64 8, ptr {{.*}}, ptr {{.*}}, i32 {{.*}})
+!$omp atomic read
+  c41 = c42
+  
+  ! Double precision complex: 16 bytes (this was broken before the fix)
+  ! CHECK: call void @__atomic_load(i64 16, ptr {{.*}}, ptr {{.*}}, i32 {{.*}})
+!$omp atomic read
+  c81 = c82
+
+end program atomic_read_complex

flang/test/Lower/OpenMP/atomic-write-complex.f90

@@ -0,0 +1,34 @@
+! Test lowering of atomic write to LLVM IR for complex types.
+! This is a regression test for issue #165184.
+
+! RUN: %flang_fc1 -emit-llvm -fopenmp -o - %s | FileCheck %s
+
+! Test that atomic write operations with complex types emit the correct
+! size parameter to __atomic_store:
+! - complex(4) (8 bytes total): should call __atomic_store(i64 8, ...)
+! - complex(8) (16 bytes total): should call __atomic_store(i64 16, ...)
+
+program atomic_write_complex
+  implicit none
+
+  ! Test complex(4) - single precision (8 bytes)
+  complex(4) :: c41, c42
+  ! Test complex(8) - double precision (16 bytes)  
+  complex(8) :: c81, c82
+  
+  c42 = (1.0_4, 1.0_4)
+  c82 = (1.0_8, 1.0_8)
+
+  ! CHECK-LABEL: define {{.*}} @_QQmain
+  
+  ! Single precision complex: 8 bytes
+  ! CHECK: call void @__atomic_store(i64 8, ptr {{.*}}, ptr {{.*}}, i32 {{.*}})
+!$omp atomic write
+  c41 = c42
+  
+  ! Double precision complex: 16 bytes (this was broken before the fix)
+  ! CHECK: call void @__atomic_store(i64 16, ptr {{.*}}, ptr {{.*}}, i32 {{.*}})
+!$omp atomic write
+  c81 = c82
+
+end program atomic_write_complex

llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

@@ -9338,9 +9338,8 @@ OpenMPIRBuilder::createAtomicRead(const LocationDescription &Loc,
     // target does not support `atomicrmw` of the size of the struct
     LoadInst *OldVal = Builder.CreateLoad(XElemTy, X.Var, "omp.atomic.read");
     OldVal->setAtomic(AO);
-    const DataLayout &LoadDL = OldVal->getModule()->getDataLayout();
-    unsigned LoadSize =
-        LoadDL.getTypeStoreSize(OldVal->getPointerOperand()->getType());
+    const DataLayout &DL = OldVal->getModule()->getDataLayout();
+    unsigned LoadSize = DL.getTypeStoreSize(XElemTy);
     OpenMPIRBuilder::AtomicInfo atomicInfo(
         &Builder, XElemTy, LoadSize * 8, LoadSize * 8, OldVal->getAlign(),
         OldVal->getAlign(), true /* UseLibcall */, AllocaIP, X.Var);
@@ -9384,9 +9383,8 @@ OpenMPIRBuilder::createAtomicWrite(const LocationDescription &Loc,
     XSt->setAtomic(AO);
   } else if (XElemTy->isStructTy()) {
     LoadInst *OldVal = Builder.CreateLoad(XElemTy, X.Var, "omp.atomic.read");
-    const DataLayout &LoadDL = OldVal->getModule()->getDataLayout();
-    unsigned LoadSize =
-        LoadDL.getTypeStoreSize(OldVal->getPointerOperand()->getType());
+    const DataLayout &DL = OldVal->getModule()->getDataLayout();
+    unsigned LoadSize = DL.getTypeStoreSize(XElemTy);
     OpenMPIRBuilder::AtomicInfo atomicInfo(
         &Builder, XElemTy, LoadSize * 8, LoadSize * 8, OldVal->getAlign(),
         OldVal->getAlign(), true /* UseLibcall */, AllocaIP, X.Var);