[flang] Record the original name of a function during ExternalNameCov…

…ersion (#74065)

We pass TBAA alias information with separate TBAA trees per function (to
prevent incorrect alias information after inlining). These TBAA trees
are identified by a unique string per function. Naturally, we use the
mangled name of the function.

TBAA tags are added in two places: during a dedicated pass relatively
early (structured control flow makes fir::AliasAnalysis more accurate),
then again during CodeGen (when implied box loads and stores become
visible). In between these two passes, the ExternalNameConversion pass
changes the name of some functions.

These functions with changed names previously ended up with separate
TBAA trees from the TBAA tags pass and from CodeGen - leading LLVM to
think that all data accesses alias with all descriptor accesses.

This patch solves this by storing the original name of a function in an
attribute during the ExternalNameConversion pass, and using the name
from that attribute when creating TBAA trees during CodeGen.

flang/include/flang/Optimizer/Analysis/TBAAForest.h

@@ -9,9 +9,11 @@
 #ifndef FORTRAN_OPTIMIZER_ANALYSIS_TBAA_FOREST_H
 #define FORTRAN_OPTIMIZER_ANALYSIS_TBAA_FOREST_H
 
+#include "flang/Optimizer/Dialect/FIROpsSupport.h"
 #include "mlir/Dialect/Func/IR/FuncOps.h"
 #include "mlir/Dialect/LLVMIR/LLVMAttrs.h"
 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
+#include "mlir/IR/Attributes.h"
 #include "mlir/IR/MLIRContext.h"
 #include "llvm/ADT/DenseMap.h"
 #include <string>
@@ -82,6 +84,12 @@ class TBAAForrest {
     return getFuncTree(func.getSymNameAttr());
   }
   inline const TBAATree &operator[](mlir::LLVM::LLVMFuncOp func) {
+    // the external name conversion pass may rename some functions. Their old
+    // name must be used so that we add to the tbaa tree added in the FIR pass
+    mlir::Attribute attr = func->getAttr(getInternalFuncNameAttrName());
+    if (attr) {
+      return getFuncTree(attr.cast<mlir::StringAttr>());
+    }
     return getFuncTree(func.getSymNameAttr());
   }
 

flang/include/flang/Optimizer/Dialect/FIROpsSupport.h

@@ -93,6 +93,12 @@ static constexpr llvm::StringRef getInternalProcedureAttrName() {
   return "fir.internal_proc";
 }
 
+/// Attribute containing the original name of a function from before the
+/// ExternalNameConverision pass runs
+static constexpr llvm::StringRef getInternalFuncNameAttrName() {
+  return "fir.internal_name";
+}
+
 /// Does the function, \p func, have a host-associations tuple argument?
 /// Some internal procedures may have access to host procedure variables.
 bool hasHostAssociationArgument(mlir::func::FuncOp func);

flang/lib/Optimizer/Transforms/ExternalNameConversion.cpp

@@ -9,11 +9,13 @@
 #include "flang/Common/Fortran.h"
 #include "flang/Optimizer/Dialect/FIRDialect.h"
 #include "flang/Optimizer/Dialect/FIROps.h"
+#include "flang/Optimizer/Dialect/FIROpsSupport.h"
 #include "flang/Optimizer/Support/InternalNames.h"
 #include "flang/Optimizer/Transforms/Passes.h"
 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
 #include "mlir/Dialect/OpenACC/OpenACC.h"
 #include "mlir/Dialect/OpenMP/OpenMPDialect.h"
+#include "mlir/IR/Attributes.h"
 #include "mlir/IR/SymbolTable.h"
 #include "mlir/Pass/Pass.h"
 #include "mlir/Transforms/DialectConversion.h"
@@ -75,7 +77,8 @@ struct MangleNameOnFuncOp : public mlir::OpRewritePattern<mlir::func::FuncOp> {
                   mlir::PatternRewriter &rewriter) const override {
     mlir::LogicalResult ret = success();
     rewriter.startRootUpdate(op);
-    auto result = fir::NameUniquer::deconstruct(op.getSymName());
+    llvm::StringRef oldName = op.getSymName();
+    auto result = fir::NameUniquer::deconstruct(oldName);
     if (fir::NameUniquer::isExternalFacingUniquedName(result)) {
       auto newSymbol =
           rewriter.getStringAttr(mangleExternalName(result, appendUnderscore));
@@ -86,6 +89,9 @@ struct MangleNameOnFuncOp : public mlir::OpRewritePattern<mlir::func::FuncOp> {
 
       op.setSymNameAttr(newSymbol);
       mlir::SymbolTable::setSymbolName(op, newSymbol);
+
+      op->setAttr(fir::getInternalFuncNameAttrName(),
+                  mlir::StringAttr::get(op->getContext(), oldName));
     }
 
     updateEarlyOutliningParentName(op, appendUnderscore);

flang/test/Fir/external-mangling.fir

@@ -49,8 +49,8 @@ func.func private @_QPbar2(!fir.ref<f32>)
 
 // LLVMIR-UNDER: llvm.mlir.global common @a_(dense<0> : vector<4xi8>) {{.*}} : !llvm.array<4 x i8>
 // LLVMIR-UNDER: llvm.mlir.global common @__BLNK__(dense<0> : vector<4xi8>) {{.*}}  : !llvm.array<4 x i8>
-// LLVMIR-UNDER: llvm.func @bar_(!llvm.ptr) attributes {sym_visibility = "private"}
-// LLVMIR-UNDER: llvm.func @bar2_(!llvm.ptr) attributes {sym_visibility = "private"}
+// LLVMIR-UNDER: llvm.func @bar_(!llvm.ptr) attributes {fir.internal_name = "_QPbar", sym_visibility = "private"}
+// LLVMIR-UNDER: llvm.func @bar2_(!llvm.ptr) attributes {fir.internal_name = "_QPbar2", sym_visibility = "private"}
 
 // LLVMIR-NOUNDER: %{{.*}} = llvm.mlir.addressof @a : !llvm.ptr
 // LLVMIR-NOUNDER: %{{.*}} = llvm.mlir.addressof @__BLNK__ : !llvm.ptr
@@ -59,8 +59,8 @@ func.func private @_QPbar2(!fir.ref<f32>)
 
 // LLVMIR-NOUNDER: llvm.mlir.global common @a(dense<0> : vector<4xi8>) {{.*}} : !llvm.array<4 x i8>
 // LLVMIR-NOUNDER: llvm.mlir.global common @__BLNK__(dense<0> : vector<4xi8>) {{.*}}  : !llvm.array<4 x i8>
-// LLVMIR-NOUNDER: llvm.func @bar(!llvm.ptr) attributes {sym_visibility = "private"}
-// LLVMIR-NOUNDER: llvm.func @bar2(!llvm.ptr) attributes {sym_visibility = "private"}
+// LLVMIR-NOUNDER: llvm.func @bar(!llvm.ptr) attributes {fir.internal_name = "_QPbar", sym_visibility = "private"}
+// LLVMIR-NOUNDER: llvm.func @bar2(!llvm.ptr) attributes {fir.internal_name = "_QPbar2", sym_visibility = "private"}
 
 // ----- 
 
@@ -96,5 +96,5 @@ func.func @_QPwriteindex_omp_outline_0() attributes {omp.outline_parent_name = "
    return
 }
 
-// CHECK-UNDER: attributes {omp.outline_parent_name = "writeindex_"}
-// CHECK-NOUNDER: attributes {omp.outline_parent_name = "writeindex"}
+// CHECK-UNDER: attributes {fir.internal_name = "_QPwriteindex_omp_outline_0", omp.outline_parent_name = "writeindex_"}
+// CHECK-NOUNDER: attributes {fir.internal_name = "_QPwriteindex_omp_outline_0", omp.outline_parent_name = "writeindex"}