[Flang][Driver] Add a flag to control zero initialization of global v… (#122144)

…ariables

Patch adds a flag to control zero initialization of global variables
without default initialization. The default is to zero initialize.

Author: kiranchandramohan

clang/include/clang/Driver/Options.td

@@ -3505,6 +3505,11 @@ def fno_struct_path_tbaa : Flag<["-"], "fno-struct-path-tbaa">, Group<f_Group>;
 def fno_strict_enums : Flag<["-"], "fno-strict-enums">, Group<f_Group>;
 def fno_strict_overflow : Flag<["-"], "fno-strict-overflow">, Group<f_Group>,
   Visibility<[ClangOption, FlangOption]>;
+defm init_global_zero : BoolOptionWithoutMarshalling<"f", "init-global-zero",
+  PosFlag<SetTrue, [], [FlangOption, FC1Option],
+          "Zero initialize globals without default initialization (default)">,
+  NegFlag<SetFalse, [], [FlangOption, FC1Option],
+          "Do not zero initialize globals without default initialization">>;
 def fno_pointer_tbaa : Flag<["-"], "fno-pointer-tbaa">, Group<f_Group>;
 def fno_temp_file : Flag<["-"], "fno-temp-file">, Group<f_Group>,
   Visibility<[ClangOption, CC1Option, CLOption, DXCOption]>, HelpText<

clang/lib/Driver/ToolChains/Flang.cpp

@@ -155,7 +155,9 @@ void Flang::addCodegenOptions(const ArgList &Args,
                    options::OPT_flang_deprecated_no_hlfir,
                    options::OPT_fno_ppc_native_vec_elem_order,
                    options::OPT_fppc_native_vec_elem_order,
-                   options::OPT_ftime_report, options::OPT_ftime_report_EQ});
+                   options::OPT_finit_global_zero,
+                   options::OPT_fno_init_global_zero, options::OPT_ftime_report,
+                   options::OPT_ftime_report_EQ});
 }
 
 void Flang::addPicOptions(const ArgList &Args, ArgStringList &CmdArgs) const {

flang/include/flang/Lower/LoweringOptions.def

@@ -44,5 +44,8 @@ ENUM_LOWERINGOPT(IntegerWrapAround, unsigned, 1, 0)
 /// If false, assume that the shapes/types/allocation-status match.
 ENUM_LOWERINGOPT(ReallocateLHS, unsigned, 1, 1)
 
+/// If true, initialize globals without initialization to zero.
+/// On by default.
+ENUM_LOWERINGOPT(InitGlobalZero, unsigned, 1, 1)
 #undef LOWERINGOPT
 #undef ENUM_LOWERINGOPT

flang/lib/Frontend/CompilerInvocation.cpp

@@ -1373,6 +1373,14 @@ bool CompilerInvocation::createFromArgs(
     invoc.loweringOpts.setNoPPCNativeVecElemOrder(true);
   }
 
+  // -f[no-]init-global-zero
+  if (args.hasFlag(clang::driver::options::OPT_finit_global_zero,
+                   clang::driver::options::OPT_fno_init_global_zero,
+                   /*default=*/true))
+    invoc.loweringOpts.setInitGlobalZero(true);
+  else
+    invoc.loweringOpts.setInitGlobalZero(false);
+
   // Preserve all the remark options requested, i.e. -Rpass, -Rpass-missed or
   // -Rpass-analysis. This will be used later when processing and outputting the
   // remarks generated by LLVM in ExecuteCompilerInvocation.cpp.

flang/lib/Lower/ConvertVariable.cpp

@@ -635,7 +635,11 @@ static fir::GlobalOp defineGlobal(Fortran::lower::AbstractConverter &converter,
       global.setLinkName(builder.createCommonLinkage());
     Fortran::lower::createGlobalInitialization(
         builder, global, [&](fir::FirOpBuilder &builder) {
-          mlir::Value initValue = builder.create<fir::ZeroOp>(loc, symTy);
+          mlir::Value initValue;
+          if (converter.getLoweringOptions().getInitGlobalZero())
+            initValue = builder.create<fir::ZeroOp>(loc, symTy);
+          else
+            initValue = builder.create<fir::UndefOp>(loc, symTy);
           builder.create<fir::HasValueOp>(loc, initValue);
         });
   }

flang/test/Driver/fno-zero-init.f90

@@ -0,0 +1,9 @@
+! Check that the driver passes through -f[no-]init-global-zero:
+! RUN: %flang -### -S -finit-global-zero %s -o - 2>&1 | FileCheck --check-prefix=CHECK-POS %s
+! RUN: %flang -### -S -fno-init-global-zero %s -o - 2>&1 | FileCheck --check-prefix=CHECK-NEG %s
+! Check that the compiler accepts -f[no-]init-global-zero:
+! RUN: %flang_fc1 -emit-hlfir -finit-global-zero %s -o -
+! RUN: %flang_fc1 -emit-hlfir -fno-init-global-zero %s -o -
+
+! CHECK-POS: "-fc1"{{.*}}"-finit-global-zero"
+! CHECK-NEG: "-fc1"{{.*}}"-fno-init-global-zero"

flang/test/Lower/zero_init.f90

@@ -0,0 +1,17 @@
+! RUN: %flang_fc1 -emit-hlfir -o - %s | FileCheck --check-prefix=CHECK-DEFAULT %s
+! RUN: %flang_fc1 -finit-global-zero -emit-hlfir -o - %s | FileCheck --check-prefix=CHECK-DEFAULT %s
+! RUN: %flang_fc1 -fno-init-global-zero -emit-hlfir -o - %s | FileCheck --check-prefix=CHECK-NO-ZERO-INIT %s
+
+module m1
+  real :: x
+end module m1
+
+!CHECK-DEFAULT: fir.global @_QMm1Ex : f32 {
+!CHECK-DEFAULT:   %[[UNDEF:.*]] = fir.zero_bits f32
+!CHECK-DEFAULT:   fir.has_value %[[UNDEF]] : f32
+!CHECK-DEFAULT: }
+
+!CHECK-NO-ZERO-INIT: fir.global @_QMm1Ex : f32 {
+!CHECK-NO-ZERO-INIT:   %[[UNDEF:.*]] = fir.undefined f32
+!CHECK-NO-ZERO-INIT:   fir.has_value %[[UNDEF]] : f32
+!CHECK-NO-ZERO-INIT: }

flang/test/Lower/zero_init_default_init.f90

@@ -0,0 +1,19 @@
+! RUN: %flang_fc1 -emit-hlfir -o - %s | FileCheck %s
+! RUN: %flang_fc1 -finit-global-zero -emit-hlfir -o - %s | FileCheck %s
+! RUN: %flang_fc1 -fno-init-global-zero -emit-hlfir -o - %s | FileCheck %s
+
+! Test that the flag does not affect globals with default init
+
+module m2
+  type val
+    integer :: my_val = 1
+  end type val
+  type(val) :: v1
+end module m2
+
+!CHECK:  fir.global @_QMm2Ev1 : !fir.type<_QMm2Tval{my_val:i32}> {
+!CHECK:    %[[V1:.*]] = fir.undefined !fir.type<_QMm2Tval{my_val:i32}>
+!CHECK:    %[[ONE:.*]] = arith.constant 1 : i32
+!CHECK:    %[[V1_INIT:.*]] = fir.insert_value %[[V1]], %[[ONE]], ["my_val", !fir.type<_QMm2Tval{my_val:i32}>] : (!fir.type<_QMm2Tval{my_val:i32}>, i32) -> !fir.type<_QMm2Tval{my_val:i32}>
+!CHECK:    fir.has_value %[[V1_INIT]] : !fir.type<_QMm2Tval{my_val:i32}>
+!CHECK:  }