[arm] Simplify run-time CPU selection.

src/flag-definitions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 101 matching lines @@
   bool has_value;
   bool value;
 };
 #endif
 
 #ifdef DEBUG
 #define DEBUG_BOOL true
 #else
 #define DEBUG_BOOL false
 #endif
-#if (defined CAN_USE_VFP3_INSTRUCTIONS) || !(defined ARM_TEST_NO_FEATURE_PROBE)
-#define ENABLE_VFP3_DEFAULT true
+
+// Supported ARM configurations are:
+//  "armv6":       ARMv6 + VFPv2
+//  "armv7":       ARMv7 + VFPv3-D32 + NEON
+//  "armv7+sudiv": ARMv7 + VFPv4-D32 + NEON + SUDIV
+//  "armv8":       ARMv8 (including all of the above)
+#if !defined(ARM_TEST_NO_FEATURE_PROBE) || \

[Michael Achenbach, 2016/08/12 10:16:37]

Why is only the first case checking for ARM_TEST_NO_FEATURE_PROBE?

+    (defined(CAN_USE_ARMV8_INSTRUCTIONS) && \
+     defined(CAN_USE_ARMV7_INSTRUCTIONS) && \
+     defined(CAN_USE_SUDIV) && \
+     defined(CAN_USE_NEON) && \
+     defined(CAN_USE_VFP3_INSTRUCTIONS))
+# define ARM_ARCH_DEFAULT "armv8"
+#elif defined(CAN_USE_ARMV7_INSTRUCTIONS) && \
+      defined(CAN_USE_SUDIV) && \
+      defined(CAN_USE_NEON) && \
+      defined(CAN_USE_VFP3_INSTRUCTIONS)
+# define ARM_ARCH_DEFAULT "armv7+sudiv"
+#elif defined(CAN_USE_ARMV7_INSTRUCTIONS) && \
+      defined(CAN_USE_NEON) && \
+      defined(CAN_USE_VFP3_INSTRUCTIONS)
+# define ARM_ARCH_DEFAULT "armv7"
 #else
-#define ENABLE_VFP3_DEFAULT false
+# define ARM_ARCH_DEFAULT "armv6"

[Michael Achenbach, 2016/08/12 10:16:37]

Suggestion: Maybe better raise an error for incorrect definitions? (Maybe in a
separate CL in case we hit that error anywhere and would block this CL).

Right now we'd always end up with armv6 for incorrect cases, e.g. if somebody
defines ARMV8 but not ARMV7.

 #endif
-#if (defined CAN_USE_ARMV7_INSTRUCTIONS) || !(defined ARM_TEST_NO_FEATURE_PROBE)
-#define ENABLE_ARMV7_DEFAULT true
-#else
-#define ENABLE_ARMV7_DEFAULT false
-#endif
-#if (defined CAN_USE_ARMV8_INSTRUCTIONS) || !(defined ARM_TEST_NO_FEATURE_PROBE)
-#define ENABLE_ARMV8_DEFAULT true
-#else
-#define ENABLE_ARMV8_DEFAULT false
-#endif
-#if (defined CAN_USE_VFP32DREGS) || !(defined ARM_TEST_NO_FEATURE_PROBE)
-#define ENABLE_32DREGS_DEFAULT true
-#else
-#define ENABLE_32DREGS_DEFAULT false
-#endif
-#if (defined CAN_USE_NEON) || !(defined ARM_TEST_NO_FEATURE_PROBE)
-# define ENABLE_NEON_DEFAULT true
-#else
-# define ENABLE_NEON_DEFAULT false
-#endif
+
 #ifdef V8_OS_WIN
 # define ENABLE_LOG_COLOUR false
 #else
 # define ENABLE_LOG_COLOUR true
 #endif
 
 #define DEFINE_BOOL(nam, def, cmt) FLAG(BOOL, bool, nam, def, cmt)
 #define DEFINE_BOOL_READONLY(nam, def, cmt) \
   FLAG_READONLY(BOOL, bool, nam, def, cmt)
 #define DEFINE_MAYBE_BOOL(nam, cmt) \
@@ skipping 394 matching lines @@
             "enable use of SSE4.1 instructions if available")
 DEFINE_BOOL(enable_sahf, true,
             "enable use of SAHF instruction if available (X64 only)")
 DEFINE_BOOL(enable_avx, true, "enable use of AVX instructions if available")
 DEFINE_BOOL(enable_fma3, true, "enable use of FMA3 instructions if available")
 DEFINE_BOOL(enable_bmi1, true, "enable use of BMI1 instructions if available")
 DEFINE_BOOL(enable_bmi2, true, "enable use of BMI2 instructions if available")
 DEFINE_BOOL(enable_lzcnt, true, "enable use of LZCNT instruction if available")
 DEFINE_BOOL(enable_popcnt, true,
             "enable use of POPCNT instruction if available")
-DEFINE_BOOL(enable_vfp3, ENABLE_VFP3_DEFAULT,

[Michael Achenbach, 2016/08/05 13:17:12]

If we pass this flag, will d8 fail or just warn?

We're referencing a few flags in the infrastructure:
https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/v8/config...
https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/v8/builde...
https://cs.chromium.org/chromium/src/v8/tools/run-tests.py?q=%22--novfp3%22&s...

Maybe we should discuss the current cases and figure out if they are all useful
- or will stay useful.

[Michael Achenbach, 2016/08/12 10:16:37]

Clarification: Warning is desired so that we can make this change without
breaking any obsolete bots. We can update the bots later.

-            "enable use of VFP3 instructions if available")
-DEFINE_BOOL(enable_armv7, ENABLE_ARMV7_DEFAULT,
-            "enable use of ARMv7 instructions if available (ARM only)")
-DEFINE_BOOL(enable_armv8, ENABLE_ARMV8_DEFAULT,
-            "enable use of ARMv8 instructions if available (ARM 32-bit only)")
-DEFINE_BOOL(enable_neon, ENABLE_NEON_DEFAULT,
-            "enable use of NEON instructions if available (ARM only)")
-DEFINE_BOOL(enable_sudiv, true,
-            "enable use of SDIV and UDIV instructions if available (ARM only)")
+DEFINE_STRING(arm_arch, ARM_ARCH_DEFAULT,
+              "generate instructions for the selected ARM architecture if "
+              "available: armv6, armv7, armv7+sudiv or armv8")
 DEFINE_BOOL(enable_movw_movt, false,
-            "enable loading 32-bit constant by means of movw/movt "
-            "instruction pairs (ARM only)")
-DEFINE_BOOL(enable_32dregs, ENABLE_32DREGS_DEFAULT,
-            "enable use of d16-d31 registers on ARM - this requires VFP3")
+            "prefer to load 32-bit constants using movw/movt instruction pairs "
+            "(ARM only)")
 DEFINE_BOOL(enable_vldr_imm, false,
             "enable use of constant pools for double immediate (ARM only)")
 DEFINE_BOOL(force_long_branches, false,
             "force all emitted branches to be in long mode (MIPS/PPC only)")
 DEFINE_STRING(mcpu, "auto", "enable optimization for specific cpu")
 
 // regexp-macro-assembler-*.cc
 DEFINE_BOOL(enable_regexp_unaligned_accesses, true,
             "enable unaligned accesses for the regexp engine")
 
-DEFINE_IMPLICATION(enable_armv8, enable_vfp3)
-DEFINE_IMPLICATION(enable_armv8, enable_neon)
-DEFINE_IMPLICATION(enable_armv8, enable_32dregs)
-DEFINE_IMPLICATION(enable_armv8, enable_sudiv)
-
 // bootstrapper.cc
 DEFINE_STRING(expose_natives_as, NULL, "expose natives in global object")
 DEFINE_STRING(expose_debug_as, NULL, "expose debug in global object")
 DEFINE_BOOL(expose_free_buffer, false, "expose freeBuffer extension")
 DEFINE_BOOL(expose_gc, false, "expose gc extension")
 DEFINE_STRING(expose_gc_as, NULL,
               "expose gc extension under the specified name")
 DEFINE_IMPLICATION(expose_gc_as, expose_gc)
 DEFINE_BOOL(expose_externalize_string, false,
             "expose externalize string extension")
@@ skipping 608 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA