[clang] [Driver] Teach Barmetal toolchain about GCC installation(1/3) (PR #121829)

[Petr Hosek via cfe-commits]

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@@ -110,20 +111,93 @@ static std::string computeBaseSysRoot(const Driver &D, bool IncludeTriple) {
   return std::string(SysRootDir);
 }
 
+// GCC sysroot here means form sysroot from either --gcc-install-dir, or from
+// --gcc-toolchain or if the toolchain is installed alongside clang in
+// bin/../<TargetTriple> directory if it is not explicitly specified on the
+// command line through `--sysroot` option. libc here will be newlib.
+std::string BareMetal::computeGCCSysRoot() const {
+  if (!getDriver().SysRoot.empty())
+    return getDriver().SysRoot;
+
+  SmallString<128> SysRootDir;
+  if (GCCInstallation.isValid()) {
+    StringRef LibDir = GCCInstallation.getParentLibPath();
+    StringRef TripleStr = GCCInstallation.getTriple().str();
+    llvm::sys::path::append(SysRootDir, LibDir, "..", TripleStr);
+  } else {
+    // Use the triple as provided to the driver. Unlike the parsed triple
+    // this has not been normalized to always contain every field.
+    llvm::sys::path::append(SysRootDir, getDriver().Dir, "..",
+                            getDriver().getTargetTriple());
+  }
+
+  if (!llvm::sys::fs::exists(SysRootDir))
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petrhosek wrote:

I believe the underlying issue is that BareMetal and RISCVToolchain original authors made different choices when it comes to the default sysroot location:

* BareMetal uses the `bin/../lib/clang-runtimes/<TargetTriple>` directory.
* RISCVToolchain uses the `bin/../<TargetTriple>` directory.

Unless we deprecate one (or both) of these and force everyone to switch to a common one, I don't think we can avoid the directory check.

I'd be in favor of unifying on a single location sooner rather than later even if it's going to require a migration for some users. This would be probably best discussed in an RFC though.

https://github.com/llvm/llvm-project/pull/121829