arch-x86: Adding warning for movnti

We are ignoring the non-temporal hint here, and implementing this
instruction as a cacheable instruction.

This change adds a warning to let user know about this workaround.

Change-Id: I2e40437a44282fe9cf7772a25a8870bd8729a6ed
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20428
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

src/arch/x86/isa/decoder/two_byte_opcodes.isa

@@ -878,6 +878,8 @@
                     // no prefix
                     0x0: decode OPCODE_OP_BOTTOM3 {
                         0x2: CMPPS(Vo,Wo,Ib);
+                        //Non-temporal hint is ignored since we don't have
+                        //proper support for it in the memory system.
                         0x3: MOVNTI(Mdp,Gdp);
                         0x4: PINSRW(Pq,Ew,Ib);
                         0x5: PEXTRW(Gd,PRq,Ib);

src/arch/x86/isa/insts/general_purpose/data_transfer/move.py

@@ -333,10 +333,12 @@ processDescriptor:
 };
 
 def macroop MOVNTI_M_R {
+    warn_once "MOVNTI: Ignoring non-temporal hint, modeling as cacheable!"
     st reg, seg, sib, disp
 };
 
 def macroop MOVNTI_P_R {
+    warn_once "MOVNTI_P: Ignoring non-temporal hint, modeling as cacheable!"
     rdip t7
     st reg, seg, riprel, disp
 };