[clang] [flang] [flang] Add -f[no-]slp-vectorize flags (PR #132801)

[Tarun Prabhu via cfe-commits]

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@@ -161,6 +161,14 @@ void Flang::addCodegenOptions(const ArgList &Args,
                    options::OPT_fno_vectorize, enableVec))
     CmdArgs.push_back("-vectorize-loops");
 
+  // -fslp-vectorize is enabled based on the optimization level selected.
+  bool EnableSLPVec = shouldEnableVectorizerAtOLevel(Args, true);
+  OptSpecifier SLPVectAliasOption =
+      EnableSLPVec ? options::OPT_O_Group : options::OPT_fslp_vectorize;
+  if (Args.hasFlag(options::OPT_fslp_vectorize, SLPVectAliasOption,
+                   options::OPT_fno_slp_vectorize, EnableSLPVec))
+    CmdArgs.push_back("-vectorize-slp");
+
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tarunprabhu wrote:

I think this block and the one above it that adds the `-vectorize-loops` `-fc1` option can be shared between `clang` and `flang`. The corresponding code in clang is [here](https://github.com/llvm/llvm-project/blob/8d3dc1ed5656a3e69e4195d58684a7f4bf0ff5cc/clang/lib/Driver/ToolChains/Clang.cpp#L7600). Such code is typically moved to `clang/lib/Driver/ToolChains/CommonArgs.cpp`. It's probably better to share it rather than duplicate it. See, for example, [this](https://github.com/llvm/llvm-project/pull/109210/files)

https://github.com/llvm/llvm-project/pull/132801