PPC/S390 [simulator] Use bit_cast instead of reinterpret_cast

The following bit casting method using reinterpret_cast
has undefined behaviour:
```
int a = 1;
float b = *reinterpret_cast<float*>(&a);
```
Above breaks the strict aliasing rule which indicates:
> dereferencing pointers to objects of different types will
never refer to the same memory location.

More information can be found under src/base/macros.h.

`bit_cast` here is implemented with `memcpy` behind the scenes.
C++20 will have this feature included by default.

Change-Id: I69ffdbeba6db64e24b268d838ea1d863fcd9121d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2889331Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#74513}

src/execution/ppc/simulator-ppc.cc

@@ -1138,7 +1138,7 @@ void Simulator::SoftwareInterrupt(Instruction* instr) {
         SimulatorRuntimeDirectGetterCall target =
             reinterpret_cast<SimulatorRuntimeDirectGetterCall>(external);
         if (!ABI_PASSES_HANDLES_IN_REGS) {
-          arg[0] = *(reinterpret_cast<intptr_t*>(arg[0]));
+          arg[0] = bit_cast<intptr_t>(arg[0]);
         }
         target(arg[0], arg[1]);
       } else if (redirection->type() ==
@@ -1157,7 +1157,7 @@ void Simulator::SoftwareInterrupt(Instruction* instr) {
         SimulatorRuntimeProfilingGetterCall target =
             reinterpret_cast<SimulatorRuntimeProfilingGetterCall>(external);
         if (!ABI_PASSES_HANDLES_IN_REGS) {
-          arg[0] = *(reinterpret_cast<intptr_t*>(arg[0]));
+          arg[0] = bit_cast<intptr_t>(arg[0]);
         }
         target(arg[0], arg[1], Redirection::ReverseRedirection(arg[2]));
       } else {
@@ -3913,8 +3913,7 @@ void Simulator::ExecuteGeneric(Instruction* instr) {
     case STVX: {
       DECODE_VX_INSTRUCTION(vrs, ra, rb, S)
       GET_ADDRESS(ra, rb, ra_val, rb_val)
-      __int128 vrs_val =
-          *(reinterpret_cast<__int128*>(get_simd_register(vrs).int8));
+      __int128 vrs_val = bit_cast<__int128>(get_simd_register(vrs).int8);
       WriteQW((ra_val + rb_val) & 0xFFFFFFFFFFFFFFF0, vrs_val);
       break;
     }
@@ -3946,8 +3945,7 @@ void Simulator::ExecuteGeneric(Instruction* instr) {
       DECODE_VX_INSTRUCTION(vrs, ra, rb, S)
       GET_ADDRESS(ra, rb, ra_val, rb_val)
       intptr_t addr = ra_val + rb_val;
-      __int128 vrs_val =
-          *(reinterpret_cast<__int128*>(get_simd_register(vrs).int8));
+      __int128 vrs_val = bit_cast<__int128>(get_simd_register(vrs).int8);
       WriteQW(addr, vrs_val);
       break;
     }
@@ -4002,9 +4000,9 @@ void Simulator::ExecuteGeneric(Instruction* instr) {
     case XXBRQ: {
       int t = instr->RTValue();
       int b = instr->RBValue();
-      __int128 xb_val = *reinterpret_cast<__int128*>(get_simd_register(b).int8);
+      __int128 xb_val = bit_cast<__int128>(get_simd_register(b).int8);
       __int128 xb_val_reversed = __builtin_bswap128(xb_val);
-      simdr_t simdr_xb = *reinterpret_cast<simdr_t*>(&xb_val_reversed);
+      simdr_t simdr_xb = bit_cast<simdr_t>(xb_val_reversed);
       set_simd_register(t, simdr_xb);
       break;
     }
@@ -4775,7 +4773,7 @@ void Simulator::ExecuteGeneric(Instruction* instr) {
       DECODE_VX_INSTRUCTION(t, a, b, T)
       uint16_t result_bits = 0;
       unsigned __int128 src_bits =
-          *(reinterpret_cast<__int128*>(get_simd_register(a).int8));
+          bit_cast<__int128>(get_simd_register(a).int8);
       for (int i = 0; i < kSimd128Size; i++) {
         result_bits <<= 1;
         uint8_t selected_bit_index = get_simd_register_by_lane<uint8_t>(b, i);
@@ -5007,7 +5005,7 @@ void Simulator::CallInternal(Address entry) {
   // Prepare to execute the code at entry
   if (ABI_USES_FUNCTION_DESCRIPTORS) {
     // entry is the function descriptor
-    set_pc(*(reinterpret_cast<intptr_t*>(entry)));
+    set_pc(*(bit_cast<intptr_t*>(entry)));
   } else {
     // entry is the instruction address
     set_pc(static_cast<intptr_t>(entry));

src/execution/s390/simulator-s390.cc

@@ -2002,8 +2002,8 @@ void Simulator::SoftwareInterrupt(Instruction* instr) {
           (redirection->type() == ExternalReference::BUILTIN_FP_INT_CALL);
 
       // Place the return address on the stack, making the call GC safe.
-      *reinterpret_cast<intptr_t*>(get_register(sp) +
-                                   kStackFrameRASlot * kSystemPointerSize) =
+      *bit_cast<intptr_t*>(get_register(sp) +
+                           kStackFrameRASlot * kSystemPointerSize) =
           get_register(r14);
 
       intptr_t external =
@@ -2143,7 +2143,7 @@ void Simulator::SoftwareInterrupt(Instruction* instr) {
         SimulatorRuntimeDirectGetterCall target =
             reinterpret_cast<SimulatorRuntimeDirectGetterCall>(external);
         if (!ABI_PASSES_HANDLES_IN_REGS) {
-          arg[0] = *(reinterpret_cast<intptr_t*>(arg[0]));
+          arg[0] = bit_cast<intptr_t>(arg[0]);
         }
         target(arg[0], arg[1]);
       } else if (redirection->type() ==
@@ -2162,7 +2162,7 @@ void Simulator::SoftwareInterrupt(Instruction* instr) {
         SimulatorRuntimeProfilingGetterCall target =
             reinterpret_cast<SimulatorRuntimeProfilingGetterCall>(external);
         if (!ABI_PASSES_HANDLES_IN_REGS) {
-          arg[0] = *(reinterpret_cast<intptr_t*>(arg[0]));
+          arg[0] = bit_cast<intptr_t>(arg[0]);
         }
         target(arg[0], arg[1], Redirection::ReverseRedirection(arg[2]));
       } else {
@@ -2270,7 +2270,7 @@ void Simulator::SoftwareInterrupt(Instruction* instr) {
         //         }
         // #endif
       }
-      int64_t saved_lr = *reinterpret_cast<intptr_t*>(
+      int64_t saved_lr = *bit_cast<intptr_t*>(
           get_register(sp) + kStackFrameRASlot * kSystemPointerSize);
 #if (!V8_TARGET_ARCH_S390X && V8_HOST_ARCH_S390)
       // On zLinux-31, the saved_lr might be tagged with a high bit of 1.
@@ -2487,7 +2487,7 @@ void Simulator::CallInternal(Address entry, int reg_arg_count) {
   // Prepare to execute the code at entry
   if (ABI_USES_FUNCTION_DESCRIPTORS) {
     // entry is the function descriptor
-    set_pc(*(reinterpret_cast<intptr_t*>(entry)));
+    set_pc(*(bit_cast<intptr_t*>(entry)));
   } else {
     // entry is the instruction address
     set_pc(static_cast<intptr_t>(entry));
@@ -2609,7 +2609,7 @@ intptr_t Simulator::CallImpl(Address entry, int argument_count,
 // Prepare to execute the code at entry
 #if ABI_USES_FUNCTION_DESCRIPTORS
   // entry is the function descriptor
-  set_pc(*(reinterpret_cast<intptr_t*>(entry)));
+  set_pc(*(bit_cast<intptr_t*>(entry)));
 #else
   // entry is the instruction address
   set_pc(static_cast<intptr_t>(entry));
@@ -3136,12 +3136,12 @@ EVALUATE(VLREP) {
   DCHECK_OPCODE(VLREP);
   DECODE_VRX_INSTRUCTION(r1, x2, b2, d2, m3);
   intptr_t addr = GET_ADDRESS(x2, b2, d2);
-#define CASE(i, type)                                                         \
-  case i: {                                                                   \
-    FOR_EACH_LANE(j, type) {                                                  \
-      set_simd_register_by_lane<type>(r1, j, *reinterpret_cast<type*>(addr)); \
-    }                                                                         \
-    break;                                                                    \
+#define CASE(i, type)                                                 \
+  case i: {                                                           \
+    FOR_EACH_LANE(j, type) {                                          \
+      set_simd_register_by_lane<type>(r1, j, *bit_cast<type*>(addr)); \
+    }                                                                 \
+    break;                                                            \
   }
   switch (m3) {
     CASE(0, uint8_t);
@@ -3952,8 +3952,7 @@ EVALUATE(VBPERM) {
   USE(m5);
   USE(m6);
   uint16_t result_bits = 0;
-  unsigned __int128 src_bits =
-      *(reinterpret_cast<__int128*>(get_simd_register(r2).int8));
+  unsigned __int128 src_bits = bit_cast<__int128>(get_simd_register(r2).int8);
   for (int i = 0; i < kSimd128Size; i++) {
     result_bits <<= 1;
     uint8_t selected_bit_index = get_simd_register_by_lane<uint8_t>(r3, i);
@@ -5494,7 +5493,7 @@ EVALUATE(LD) {
   int64_t b2_val = (b2 == 0) ? 0 : get_register(b2);
   int64_t x2_val = (x2 == 0) ? 0 : get_register(x2);
   intptr_t addr = b2_val + x2_val + d2_val;
-  int64_t dbl_val = *reinterpret_cast<int64_t*>(addr);
+  int64_t dbl_val = *bit_cast<int64_t*>(addr);
   set_fpr(r1, dbl_val);
   return length;
 }
@@ -5533,7 +5532,7 @@ EVALUATE(LE) {
   int64_t b2_val = (b2 == 0) ? 0 : get_register(b2);
   int64_t x2_val = (x2 == 0) ? 0 : get_register(x2);
   intptr_t addr = b2_val + x2_val + d2_val;
-  float float_val = *reinterpret_cast<float*>(addr);
+  float float_val = *bit_cast<float*>(addr);
   set_fpr(r1, float_val);
   return length;
 }
@@ -11208,7 +11207,7 @@ EVALUATE(LEY) {
   int64_t x2_val = (x2 == 0) ? 0 : get_register(x2);
   int64_t b2_val = (b2 == 0) ? 0 : get_register(b2);
   intptr_t addr = x2_val + b2_val + d2;
-  float float_val = *reinterpret_cast<float*>(addr);
+  float float_val = *bit_cast<float*>(addr);
   set_fpr(r1, float_val);
   return length;
 }
@@ -11220,7 +11219,7 @@ EVALUATE(LDY) {
   int64_t x2_val = (x2 == 0) ? 0 : get_register(x2);
   int64_t b2_val = (b2 == 0) ? 0 : get_register(b2);
   intptr_t addr = x2_val + b2_val + d2;
-  uint64_t dbl_val = *reinterpret_cast<uint64_t*>(addr);
+  uint64_t dbl_val = *bit_cast<uint64_t*>(addr);
   set_fpr(r1, dbl_val);
   return length;
 }