[OMPIRBuilder] Improve DIOp based expression generation.

This fixes SWDEV-534522. It was reported that build fails in certain
cases with the following error:

invalid expression
!DIExpression(DIOpArg(0, i32), DIOpSExt(i64), DIOpDeref(i64))

The problem occur with #dbg_value debug records that are generated for
the artificial variables for array with variable dimension. DIOpDeref
requires a pointer type and this fails verification.

Please note that OMPIRBuilder actually never generated this expression.
It resulted from the later transforms. This is the reason that we don't
see this problem on O0.

The fix was to not generate the DIOpDeref for non-pointer location but I
have done some more cleanup inspired by what Scott recently did for
the declare target functions. We are now only generating the DIOp
expression for variable residing in allocas.

Author: abidh

flang/test/Integration/amdgpu/debug-target-var.f90

@@ -19,8 +19,8 @@ end subroutine fff
 ! CHECK-DAG: store ptr %[[ARG2]], ptr %[[CAST2:[0-9]+]]{{.*}}
 ! CHECK-DAG: %[[CAST2]] = addrspacecast ptr addrspace(5) %[[AL2:[0-9]+]]
 ! CHECK-DAG: %[[AL2]] = alloca{{.*}}
-! CHECK-DAG: #dbg_declare(ptr %[[CAST1]], ![[X:[0-9]+]], !DIExpression(DIOpArg(0, ptr addrspace(5)), DIOpDeref(ptr), DIOpDeref(ptr)), {{.*}})
-! CHECK-DAG: #dbg_declare(ptr %[[CAST2]], ![[Y:[0-9]+]], !DIExpression(DIOpArg(0, ptr addrspace(5)), DIOpDeref(ptr), DIOpDeref(ptr)), {{.*}})
+! CHECK-DAG: #dbg_declare(ptr {{.*}}%[[AL1]], ![[X:[0-9]+]], !DIExpression(DIOpArg(0, ptr addrspace(5)), DIOpDeref(ptr), DIOpDeref(ptr)), {{.*}})
+! CHECK-DAG: #dbg_declare(ptr {{.*}}%[[AL2]], ![[Y:[0-9]+]], !DIExpression(DIOpArg(0, ptr addrspace(5)), DIOpDeref(ptr), DIOpDeref(ptr)), {{.*}})
 ! CHECK: }
 
 ! CHECK-DAG: ![[SP]] = {{.*}}!DISubprogram(name: "[[FN]]"{{.*}})

llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

@@ -6986,22 +6986,17 @@ static void FixupDebugInfoForOutlinedFunction(
       // snippet) as location of variable. The AMDGPU backend drops the debug
       // info for variable in such cases. So we change the location to alloca
       // instead.
+      if (DR->getNumVariableLocationOps() != 1u)
+        return;
+      auto Loc = DR->getVariableLocationOp(0u);
       bool PassByRef = false;
-      llvm::Type *locType = nullptr;
-      for (auto Loc : DR->location_ops()) {
-        locType = Loc->getType();
-        if (llvm::LoadInst *Load = dyn_cast<llvm::LoadInst>(Loc)) {
-          DR->replaceVariableLocationOp(Loc, Load->getPointerOperand());
-          PassByRef = true;
-        }
+      if (llvm::LoadInst *Load = dyn_cast<llvm::LoadInst>(Loc)) {
+        Loc = Load->getPointerOperand();
+        PassByRef = true;
       }
       // Add DIOps based expression. Note that we generate an extra indirection
       // if an argument is mapped by reference. The first reads the pointer
       // from alloca and 2nd read the value of the variable from that pointer.
-      llvm::DIExprBuilder ExprBuilder(Builder.getContext());
-      unsigned int allocaAS = M->getDataLayout().getAllocaAddrSpace();
-      unsigned int defaultAS = M->getDataLayout().getProgramAddressSpace();
-      ExprBuilder.append<llvm::DIOp::Arg>(0u, Builder.getPtrTy(allocaAS));
       // We have 2 options for the variables that are mapped byRef.
       // 1. Use a single indirection but change the type to the reference to the
       // original type. It will show up in the debugger as
@@ -7010,10 +7005,15 @@ static void FixupDebugInfoForOutlinedFunction(
       // 2. Use double indirection and keep the original type. It will show up
       // in debugger as "x=5". This approached is used here as it is
       // consistent with the normal fortran parameters display.
-      if (PassByRef)
-        ExprBuilder.append<llvm::DIOp::Deref>(Builder.getPtrTy(defaultAS));
-      ExprBuilder.append<llvm::DIOp::Deref>(locType);
-      DR->setExpression(ExprBuilder.intoExpression());
+      if (auto AI = dyn_cast<llvm::AllocaInst>(Loc->stripPointerCasts())) {
+        DR->replaceVariableLocationOp(0u, AI);
+        llvm::DIExprBuilder ExprBuilder(Builder.getContext());
+        ExprBuilder.append<llvm::DIOp::Arg>(0u, AI->getType());
+        if (PassByRef)
+          ExprBuilder.append<llvm::DIOp::Deref>(AI->getAllocatedType());
+        ExprBuilder.append<llvm::DIOp::Deref>(AI->getAllocatedType());
+        DR->setExpression(ExprBuilder.intoExpression());
+      }
     }
 
     DR->setVariable(GetUpdatedDIVariable(OldVar, ArgNo));