8178033: C1 crashes with -XX:UseAVX = 3: "not a mov [reg+offs], reg instruction"

Skip the EVEX prefix such that the instruction address points to the prefixed opcode.

Reviewed-by: kvn, mcberg

hotspot/src/cpu/x86/vm/assembler_x86.cpp

@@ -917,7 +917,7 @@ address Assembler::locate_operand(address inst, WhichOperand which) {
     break;
 
   case 0x62: // EVEX_4bytes
-    assert((UseAVX > 0), "shouldn't have EVEX prefix");
+    assert(VM_Version::supports_evex(), "shouldn't have EVEX prefix");
     assert(ip == inst+1, "no prefixes allowed");
     // no EVEX collisions, all instructions that have 0x62 opcodes
     // have EVEX versions and are subopcodes of 0x66

hotspot/src/cpu/x86/vm/nativeInst_x86.cpp

@@ -365,6 +365,10 @@ int NativeMovRegMem::instruction_start() const {
     NOT_LP64(assert((0xC0 & ubyte_at(1)) == 0xC0, "shouldn't have LDS and LES instructions"));
     return 3;
   }
+  if (instr_0 == instruction_EVEX_prefix_4bytes) {
+    assert(VM_Version::supports_evex(), "shouldn't have EVEX prefix");
+    return 4;
+  }
 
   // First check to see if we have a (prefixed or not) xor
   if (instr_0 >= instruction_prefix_wide_lo && // 0x40

hotspot/src/cpu/x86/vm/nativeInst_x86.hpp

@@ -356,6 +356,7 @@ class NativeMovRegMem: public NativeInstruction {
 
     instruction_VEX_prefix_2bytes       = Assembler::VEX_2bytes,
     instruction_VEX_prefix_3bytes       = Assembler::VEX_3bytes,
+    instruction_EVEX_prefix_4bytes      = Assembler::EVEX_4bytes,
 
     instruction_size                    = 4,
     instruction_offset                  = 0,