[arm] Simplify run-time CPU selection.

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 585e839d4d496293e7f900ae532483f2a84ee799..b082b39b107070e06706ef0360eac9c1cd269cdf 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -119,31 +119,32 @@ struct MaybeBoolFlag {
 #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
-#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
+# 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
+
 #ifdef V8_OS_WIN
 # define ENABLE_LOG_COLOUR false
 #else
@@ -558,21 +559,12 @@ 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,
@@ -583,11 +575,6 @@ DEFINE_STRING(mcpu, "auto", "enable optimization for specific cpu")
 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")