[clang] [clang] [ARM] Explicitly enable NEON for Windows/Darwin targets (PR #122095)

[Adam Nemet via cfe-commits]

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@@ -659,13 +659,21 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
         CPUArgFPUKind != llvm::ARM::FK_INVALID ? CPUArgFPUKind : ArchArgFPUKind;
     (void)llvm::ARM::getFPUFeatures(FPUKind, Features);
   } else {
+    bool Generic = true;
     if (!ForAS) {
       std::string CPU = arm::getARMTargetCPU(CPUName, ArchName, Triple);
+      if (CPU != "generic")
+        Generic = false;
       llvm::ARM::ArchKind ArchKind =
           arm::getLLVMArchKindForARM(CPU, ArchName, Triple);
       FPUKind = llvm::ARM::getDefaultFPU(CPU, ArchKind);
       (void)llvm::ARM::getFPUFeatures(FPUKind, Features);
     }
+    if (Generic && (Triple.isOSWindows() || Triple.isOSDarwin()) &&
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anemet wrote:

Hi @mstorsjo, this breaks Darwin when compiling assembly with armv7s which is neon-vfp4.  vfp4 instructions (e.g. vfma) are no longer recognized because you effectively downgraded neon-vfp4 to neon.  When `ForAS` you assume a "generic" CPU unconditionally rather than "swift".

https://github.com/llvm/llvm-project/pull/122095