[Clang][ARM] Enable the use of +simd and +nosimd for AArch32 Targets

`+simd` and `+nosimd` are used to enable or disable NEON Instructions
when compiling for AArch32 Targets. However, up until now, using these
has not been possible. To enable this, these options are mapped to the
relevant LLVM backend option (`+neon` and `-neon`) so it can be both
enabled and disabled successfully by the user.

Tests have been added to ensure this behaviour is maintained in the future,
along with updates to existing tests as behaviour has now changed relating
to the use of `+simd` and `+nosimd`.

As `simd` has been mapped within the ARMTargetParser.def, support for this
extension is also added for the `--print-support-extensions` command when
the target is AArch32. This will print the `simd` option, along with the
description that relates to the Neon feature. This previously was not
possible as `simd` did not have a related Feature or Negative Feature.

Author: Stylie777

clang/test/Driver/print-supported-extensions-arm.c

@@ -12,6 +12,7 @@
 // CHECK-NEXT:     dsp                 Supports DSP instructions in ARM and/or Thumb2
 // CHECK-NEXT:     mve                 Support M-Class Vector Extension with integer ops
 // CHECK-NEXT:     mve.fp              Support M-Class Vector Extension with integer and floating ops
+// CHECK-NEXT:     simd                Enable NEON instructions
 // CHECK-NEXT:     fp16                Enable half-precision floating point
 // CHECK-NEXT:     ras                 Enable Reliability, Availability and Serviceability extensions
 // CHECK-NEXT:     fp16fml             Enable full half-precision floating point fml instructions

clang/test/Preprocessor/arm-target-features.c

@@ -1027,3 +1027,11 @@
 // CHECK-R52-NEXT: #define __ARM_VFPV4__ 1
 // CHECK-R52-NOT: #define __ARM_NEON 1
 // CHECK-R52-NOT: #define __ARM_NEON__
+
+// Check that on AArch32 appropriate targets, +nosimd correctly disables NEON instructions.
+// RUN:  %clang -target arm-none-eabi -march=armv8-a+nosimd -mfloat-abi=hard -x c -E -dM -o - %s | FileCheck -check-prefix=CHECK-NOSIMD %s
+// RUN:  %clang -target arm-none-eabi -mcpu=cortex-r52+nosimd -mfloat-abi=hard -x c -E -dM -o - %s | FileCheck -check-prefix=CHECK-NOSIMD %s
+// RUN:  %clang -target arm-none-eabi -mcpu=cortex-a57+nosimd -mfloat-abi=hard -x c -E -dM -o - %s | FileCheck -check-prefix=CHECK-NOSIMD %s
+// CHECK-NOSIMD-NOT: #define __ARM_NEON 1
+// CHECK-NOSIMD-NOT: #define __ARM_NEON_FP 0x6
+// CHECK-NOSIMD-NOT: #define __ARM_NEON__ 1

llvm/docs/ReleaseNotes.md

@@ -85,6 +85,9 @@ Changes to the AMDGPU Backend
 
 Changes to the ARM Backend
 --------------------------
+* The `+nosimd` attribute is now fully supported. Previously, this had no effect when being used with
+AArch32 targets, however will now disable NEON instructions being generated. The `simd` is also now
+printed when the `--print-supported-extensions` option is used..
 
 Changes to the AVR Backend
 --------------------------

llvm/include/llvm/TargetParser/ARMTargetParser.def

@@ -229,7 +229,7 @@ ARM_ARCH_EXT_NAME("mve.fp", (ARM::AEK_DSP | ARM::AEK_MVE | ARM::AEK_FP),
                   "+mve.fp", "-mve.fp")
 ARM_ARCH_EXT_NAME("idiv", (ARM::AEK_HWDIVARM | ARM::AEK_HWDIVTHUMB), {}, {})
 ARM_ARCH_EXT_NAME("mp", ARM::AEK_MP, {}, {})
-ARM_ARCH_EXT_NAME("simd", ARM::AEK_SIMD, {}, {})
+ARM_ARCH_EXT_NAME("simd", ARM::AEK_SIMD, "+neon", "-neon")
 ARM_ARCH_EXT_NAME("sec", ARM::AEK_SEC, {}, {})
 ARM_ARCH_EXT_NAME("virt", ARM::AEK_VIRT, {}, {})
 ARM_ARCH_EXT_NAME("fp16", ARM::AEK_FP16, "+fullfp16", "-fullfp16")
@@ -334,8 +334,8 @@ ARM_CPU_NAME("cortex-r7", ARMV7R, FK_VFPV3_D16_FP16, false,
              (ARM::AEK_MP | ARM::AEK_HWDIVARM))
 ARM_CPU_NAME("cortex-r8", ARMV7R, FK_VFPV3_D16_FP16, false,
              (ARM::AEK_MP | ARM::AEK_HWDIVARM))
-ARM_CPU_NAME("cortex-r52", ARMV8R, FK_NEON_FP_ARMV8, false, ARM::AEK_NONE)
-ARM_CPU_NAME("cortex-r52plus", ARMV8R, FK_NEON_FP_ARMV8, false, ARM::AEK_NONE)
+ARM_CPU_NAME("cortex-r52", ARMV8R, FK_NEON_FP_ARMV8, false, ARM::AEK_SIMD)
+ARM_CPU_NAME("cortex-r52plus", ARMV8R, FK_NEON_FP_ARMV8, false, ARM::AEK_SIMD)
 ARM_CPU_NAME("sc300", ARMV7M, FK_NONE, false, ARM::AEK_NONE)
 ARM_CPU_NAME("cortex-m3", ARMV7M, FK_NONE, true, ARM::AEK_NONE)
 ARM_CPU_NAME("cortex-m4", ARMV7EM, FK_FPV4_SP_D16, true, ARM::AEK_NONE)

llvm/lib/TargetParser/ARMTargetParser.cpp

@@ -657,6 +657,10 @@ void ARM::PrintSupportedExtensions(StringMap<StringRef> DescMap) {
     // Extensions without a feature cannot be used with -march.
     if (!Ext.Feature.empty()) {
       std::string Description = DescMap[Ext.Name].str();
+      // With SIMD, this links to the NEON feature, so the description should be
+      // taken from here, as SIMD does not exist in TableGen.
+      if (Ext.Name == "simd")
+        Description = DescMap["neon"].str();
       outs() << "    "
              << format(Description.empty() ? "%s\n" : "%-20s%s\n",
                        Ext.Name.str().c_str(), Description.c_str());

llvm/unittests/TargetParser/TargetParserTest.cpp

@@ -318,14 +318,14 @@ INSTANTIATE_TEST_SUITE_P(
                                        ARM::AEK_HWDIVTHUMB | ARM::AEK_DSP,
                                    "7-R"),
         ARMCPUTestParams<uint64_t>("cortex-r52", "armv8-r", "neon-fp-armv8",
-                                   ARM::AEK_NONE | ARM::AEK_CRC | ARM::AEK_MP |
-                                       ARM::AEK_VIRT | ARM::AEK_HWDIVARM |
-                                       ARM::AEK_HWDIVTHUMB | ARM::AEK_DSP,
+                                   ARM::AEK_CRC | ARM::AEK_MP | ARM::AEK_VIRT |
+                                       ARM::AEK_HWDIVARM | ARM::AEK_HWDIVTHUMB |
+                                       ARM::AEK_DSP | ARM::AEK_SIMD,
                                    "8-R"),
         ARMCPUTestParams<uint64_t>("cortex-r52plus", "armv8-r", "neon-fp-armv8",
-                                   ARM::AEK_NONE | ARM::AEK_CRC | ARM::AEK_MP |
-                                       ARM::AEK_VIRT | ARM::AEK_HWDIVARM |
-                                       ARM::AEK_HWDIVTHUMB | ARM::AEK_DSP,
+                                   ARM::AEK_CRC | ARM::AEK_MP | ARM::AEK_VIRT |
+                                       ARM::AEK_HWDIVARM | ARM::AEK_HWDIVTHUMB |
+                                       ARM::AEK_DSP | ARM::AEK_SIMD,
                                    "8-R"),
         ARMCPUTestParams<uint64_t>("sc300", "armv7-m", "none",
                                    ARM::AEK_NONE | ARM::AEK_HWDIVTHUMB, "7-M"),
@@ -801,7 +801,7 @@ TEST(TargetParserTest, ARMArchExtFeature) {
                               {"fp", "nofp", nullptr, nullptr},
                               {"idiv", "noidiv", nullptr, nullptr},
                               {"mp", "nomp", nullptr, nullptr},
-                              {"simd", "nosimd", nullptr, nullptr},
+                              {"simd", "nosimd", "+neon", "-neon"},
                               {"sec", "nosec", nullptr, nullptr},
                               {"virt", "novirt", nullptr, nullptr},
                               {"fp16", "nofp16", "+fullfp16", "-fullfp16"},
@@ -1046,7 +1046,6 @@ TEST(TargetParserTest, ARMPrintSupportedExtensions) {
   EXPECT_EQ(std::string::npos, captured.find("invalid"));
   // Should not include anything that lacks a feature name. Checking a few here
   // but not all as if one is hidden correctly the rest should be.
-  EXPECT_EQ(std::string::npos, captured.find("simd"));
   EXPECT_EQ(std::string::npos, captured.find("maverick"));
   EXPECT_EQ(std::string::npos, captured.find("xscale"));
 }