[PATCH] D52705: First-pass at ARM hard/soft-float multilib driver (NOT WORKING YET)

[Peter Smith via Phabricator via cfe-commits]

peter.smith added a comment.

I think that you may be better off posting a RFC to llvm-dev to get discussion on the best approach here. It would also be good to step back a bit and consider the requirements, as it stands it looks like this might be a solution for just one particular multilib layout and we might be able to get some input on some other use cases that others may have. I personally would like to enable clang to be able to query a gcc installation to find out (and potentially cache) its multlib directories as I've been told for the Arm embedded toolchain that the directory structure is not fixed and may change at any point in the future.

Another unrelated thing that may be worth doing is to check for other places where the target might affect the code-generation independently of -mfloat-abi, I'm thinking in particular of builtin functions as this has changed a bit over the past few years.



================
Comment at: lib/Driver/ToolChains/Gnu.cpp:1441
 
+static bool findArmEABIMultilibs(const Driver &D,
+                                 const llvm::Triple &TargetTriple,
----------------
When I saw EABIMultilibs I first thought of multilib support for arm-none-eabi , I think that this may be worth renaming to something like ArmLinuxGNUEABI as this could be specific to Linux Distributions. 


================
Comment at: lib/Driver/ToolChains/Gnu.cpp:1451
+  bool DefaultHardFloat = TargetTriple.isHardFloatEABI();
+  llvm::Triple AltTriple(DefaultHardFloat ?
+                             TargetTriple.getSoftFloatArchVariant() :
----------------
AltTriple doesn't seem to be used anywhere in the rest of the function?


================
Comment at: lib/Driver/ToolChains/Gnu.cpp:1454
+                             TargetTriple.getHardFloatArchVariant());
+  // We assume the Debian libdir/includedir arrangement for armel/armhf,
+  // since Debian and its descendents are apparently the only common Linux
----------------
Another place where this is used, and clang can't yet handle, is the GCC Embedded toolchain arm-none-eabi which includes both hard and soft float abi libraries. These have a different structure to the one presented here though.   


================
Comment at: lib/Driver/ToolChains/Gnu.cpp:1458
+  // SuSE and RedHat seem to stick with hard-float only and no libdir suffix.
+  // TODO: this (and a lot of other code here) could be generalized via the
+  // output of "gcc <flags> --print-multi-os-dir".
----------------
I definitely agree here. It seems to me to be quite fragile to hard-code in directory structures of gcc toolchains or linux distributions that can, and do, vary over time.


Repository:
  rC Clang

https://reviews.llvm.org/D52705