Make __CHERI__ a synonym for __CHERI_PURE_CAPABILITY__

WARNING: This is a breaking change for hybrid code bases.

Rational: We strongly encourage all CHERI consumers to use a
pure-capability ABI whenever possible.  In order to do so more firmly,
make __CHERI__ (the shortest macro) a synonym for
__CHERI_PURE_CAPABILITY__ rather than __has_feature(capabilities).

Backwards compatible code transition:

For purecap + standard C/C++ code:
  No change required.

For hybrid + standard C/C++ code:
  __CHERI__ -> __has_feature(capabilities)

For mixed code:
  __CHERI__ -> __has_feature(capabilities)

Once the need for compatability with old compilers is passed further
simplication is possible.

For purecap + standard C/C++ code:
  __CHERI_PURE_CAPABILITY__ -> __CHERI__

For hybrid + standard C/C++ code:
  __has_feature(capabilities) && !defined(__CHERI_PURE_CAPABILITY__) ->
      __CHERI_HYBRID__

Author: brooksdavis

clang/lib/Frontend/InitPreprocessor.cpp

@@ -997,7 +997,6 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   if (TI.SupportsCapabilities()) {
     const uint64_t CapWidth = TI.getCHERICapabilityWidth();
     const uint64_t CapRange = TI.getPointerRangeForCHERICapability();
-    Builder.defineMacro("__CHERI__", "1"); // TODO: or define __CHERI__ to 128/256?
     Builder.defineMacro("__CHERI_CAPABILITY_WIDTH__", Twine(CapWidth));
     DefineTypeSizeof("__SIZEOF_CHERI_CAPABILITY__", CapWidth, TI, Builder);
     Builder.defineMacro("__CHERI_ADDRESS_BITS__", Twine(CapRange));
@@ -1012,6 +1011,8 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
     DefineTypeSize("__UINTCAP_MAX__", TI.getIntTypeByWidth(CapRange, false), TI, Builder);
 
     if (TI.areAllPointersCapabilities()) {
+      Builder.defineMacro("__CHERI__", "1");
+
       // XXXAR is there a reason we use two instead of just defining it?
       // I don't think we have any checks that rely on the value
       Builder.defineMacro("__CHERI_PURE_CAPABILITY__", "2");

clang/test/Driver/cheri/bounds-mode.c

@@ -14,6 +14,7 @@
 // RUN: %cheri_purecap_clang -E -dM -Xclang -cheri-bounds=conservative %s 2>&1 | FileCheck --check-prefixes=CHECK,SUBOBJECT-DISABLED %s
 // Without any flag subobject bounds should currently be disabled
 // RUN: %cheri_purecap_clang -E -dM %s 2>&1 | FileCheck --check-prefixes=SUBOBJECT-DISABLED %s
+// CHECK: #define __CHERI__ 1
 // CHECK: #define __CHERI_PURE_CAPABILITY__ 2
 // SUBOBJECT-DISABLED-NOT: __CHERI_SUBOBJECT_BOUNDS__
 // SUBOBJECT-SAFE: #define __CHERI_SUBOBJECT_BOUNDS__ 2

clang/test/Preprocessor/cheri-cap-sizes.c

@@ -36,9 +36,10 @@
 // CHERI128: #define _MIPS_SZCAP 128
 // CHECK: #define __CHERI_ADDRESS_BITS__ 64
 // CHERI128: #define __CHERI_CAPABILITY_WIDTH__ 128
+// PURECAP: #define __CHERI__ 1
 // PURECAP: #define __CHERI_PURE_CAPABILITY__ 2
 // MIPS-NOT: __CHERI_PURE_CAPABILITY__
-// CHECK: #define __CHERI__ 1
+// MIPS-NOT: __CHERI__
 // MIPS: #define __CHERI_HYBRID__ 1
 // Note: 64-bit range for intcap makes more sense than the full range for pointers
 // CHECK: #define __INTCAP_MAX__ 9223372036854775807L

clang/test/Preprocessor/cheri-features.c

@@ -16,7 +16,7 @@ void* __capability x = 0;
 
 #if defined(__CHERI__)
 #pragma message("__CHERI__ defined")
-// CHECK-CHERI: warning: __CHERI__ defined
+// CHECK-CHERI: warning: __CHERI__ not defined
 void* __capability y = 0;
 #else
 #pragma message("__CHERI__ not defined")

clang/test/Preprocessor/cheri-riscv-feature-flags.c

@@ -18,7 +18,6 @@
 // CHECK: #define __CHERI_CAP_PERMISSION_PERMIT_STORE_LOCAL__ 64
 // CHECK: #define __CHERI_CAP_PERMISSION_PERMIT_STORE__ 8
 // CHECK: #define __CHERI_CAP_PERMISSION_PERMIT_UNSEAL__ 512
-// CHECK: #define __CHERI__ 1
 // CHECK: #define __CHERI_HYBRID__ 1
 // CHECK32: #define __SIZEOF_CHERI_CAPABILITY__ 8
 // CHECK64: #define __SIZEOF_CHERI_CAPABILITY__ 16

clang/test/Preprocessor/init.c

@@ -355,7 +355,6 @@
 // CHERI-COMMON-NEXT: #define __CHERI_CAP_PERMISSION_PERMIT_STORE_LOCAL__ 64
 // CHERI-COMMON-NEXT: #define __CHERI_CAP_PERMISSION_PERMIT_STORE__ 8
 // CHERI-COMMON-NEXT: #define __CHERI_CAP_PERMISSION_PERMIT_UNSEAL__ 512
-// CHERI-COMMON-NEXT: #define __CHERI__ 1
 // CHERI-COMMON-NEXT: #define __CHERI_HYBRID__ 1
 // CHERI64:           #define __POINTER_WIDTH__ 32
 // CHERI128:          #define __POINTER_WIDTH__ 64
@@ -406,6 +405,7 @@
 
 // RUN: %cheri_cc1 -E -dM -ffreestanding -triple=mips64-none-none -target-abi purecap < /dev/null | FileCheck -check-prefix CHERI128-PURECAP %s
 // CHERI128-PURECAP: #define _MIPS_FPSET 32
+// CHERI128-PURECAP: #define __CHERI__ 1
 // CHERI128-PURECAP: #define __CHERI_PURE_CAPABILITY__ 2
 // CHERI128-PURECAP: #define __CHERI_SANDBOX__ 4
 // CHERI128-PURECAP: #define __INTPTR_FMTd__ "Pd"