[PATCH] D67608: [ARM] Preserve fpu behaviour for '-crypto'

[Peter Smith via Phabricator via cfe-commits]

peter.smith added a comment.

After retesting on a failing example and experimenting a bit, I think that we should only preserve +crypto with -fno-integrated-as. It would also be good to mention D66018 <https://reviews.llvm.org/D66018> and maybe add the original author as a reviewer.



================
Comment at: clang/lib/Driver/ToolChains/Arch/ARM.cpp:499
         << "crypto" << llvm::ARM::getArchName(llvm::ARM::parseArch(ArchSuffix));
-      Features.push_back("-crypto");
+      //-mfpu=crypto-neon-fp-armv8 does allow +sha2 / +aes / +crypto features,
+      // even if compiling for an cpu armv7a, if explicitly defined by the user,
----------------
Looking into this in more detail I think the comment can be made more specific. It seems like the main reason to keep +crypto is that when the non-integrated-assembler is used, then we get the directive:
```
.fpu crypto-neon-fp-armv8
```
In arm-none-eabi-as the assembler will support crypto instructions. Clang will not as any use of crypto instructions will fail due lack of v8 support.

```
With -fno-integrated-as -mfpu=crypto-neon-fp-armv8 some assemblers such as the GNU assembler will permit the use of crypto instructions as the fpu will override the architecture. We keep the crypto feature in this case to preserve compatibility. In all other cases we remove the crypto feature. 
```


================
Comment at: clang/lib/Driver/ToolChains/Arch/ARM.cpp:502
+      // so do not deactivate them.
+      if ((llvm::find(Features, "+fp-armv8") == Features.end()) ||
+          (llvm::find(Features, "+neon") == Features.end()))
----------------
I think we should only do this for -fno-integrated-as as the integrated assembler will fail if give a crypto instruction even with this change. With the integrated assembler we get:

```
error: instruction requires: armv8
        aese.8 q8, q9
```


================
Comment at: clang/test/Driver/arm-features.c:84
+// Check +crypto does not affect -march=armv7a -mfpu=crypto-neon-fp-armv8, but it does warn that +crypto has no effect
+// RUN: %clang -target arm-arm-none-eabi -march=armv7a -mfpu=crypto-neon-fp-armv8 -### -c %s 2>&1 | FileCheck -check-prefixes=CHECK-WARNONLY,ALL %s
+// RUN: %clang -target arm-arm-none-eabi -march=armv7a+aes -mfpu=crypto-neon-fp-armv8 -### -c %s 2>&1 | FileCheck -check-prefixes=CHECK-WARNONLY,ALL,CHECK-HASAES %s
----------------
arm-arm-none-eabi is a vendor specific triple? Better to use arm-none-eabi 


Repository:
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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D67608/new/

https://reviews.llvm.org/D67608