[clang] [Clang] Enable -fextend-lifetimes at -Og (PR #118026)

[David Blaikie via cfe-commits]

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@@ -1834,6 +1834,14 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
     Opts.setInlining(CodeGenOptions::NormalInlining);
   }
 
+  // If we have specified -Og and have not explicitly set -fno-extend-lifetimes,
+  // then default to -fextend-lifetimes.
+  if (Arg *A = Args.getLastArg(options::OPT_O_Group);
+      A && A->containsValue("g")) {
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dwblaikie wrote:

I'm not sure if we have a fundamental principle about how flags should work in the driver V the frontend, but yeah - in some ways the driver acts as a lowering/canonicalizer - representing flag defaults, etc. So I think the expectation that `clang -cc1 -Og` does the same thing as `clang -Og` isn't valid/not something we're striving for (& in some sense counter to what we are striving for: that all the defaults/grouping is handled by the driver, and the frontend can just think about whether a flag is enabled or disabled)

https://github.com/llvm/llvm-project/pull/118026