[flang] [clang] [flang] Enable alias tags pass by default (PR #73111)

[Tom Eccles via cfe-commits]

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@@ -242,10 +242,24 @@ static void parseCodeGenArgs(Fortran::frontend::CodeGenOptions &opts,
                    clang::driver::options::OPT_fno_loop_versioning, false))
     opts.LoopVersioning = 1;
 
-  opts.AliasAnalysis =
-      args.hasFlag(clang::driver::options::OPT_falias_analysis,
-                   clang::driver::options::OPT_fno_alias_analysis,
-                   /*default=*/false);
+  bool aliasAnalysis = false;
+  bool noAliasAnalysis = false;
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tblah wrote:

If `-falias-analysis` is specified then we should enable alias analysis even when it would not be enabled by the optimization level.

If `-fno-alias-analysis` is specified then we should not enable enable analysis even if it would be enabled by the optimization level.

This doesn't fit neatly into a single boolean, because we also need to support the state where both of these are false (indicating that we should follow the default behavior).

An alternative implementation would be a single boolean inside a std::option. Would that be clearer?

https://github.com/llvm/llvm-project/pull/73111