arch,base,cpu,dev: Get rid of the M5_DUMMY_RETURN macro.

This macro probably would have been defined to "return" in some cases,
to be put after a call to a function that doesn't return so that the
compiler wouldn't think control would reach the end of a non-void
function. It was only ever defined to expand to nothing, and now that
[[noreturn]] is a standard attribute, it should never be needed going
forward.

Change-Id: I37625eab72deeaede77f9347116b9fddd75febf7
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/35217
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/arm/utility.cc

@@ -56,13 +56,10 @@ namespace ArmISA
 uint64_t
 getArgument(ThreadContext *tc, int &number, uint16_t size, bool fp)
 {
-    if (!FullSystem) {
-        panic("getArgument() only implemented for full system mode.\n");
-        M5_DUMMY_RETURN
-    }
+    panic_if(!FullSystem,
+            "getArgument() only implemented for full system mode.");
 
-    if (fp)
-        panic("getArgument(): Floating point arguments not implemented\n");
+    panic_if(fp, "getArgument(): Floating point arguments not implemented");
 
     if (inAArch64(tc)) {
         if (size == (uint16_t)(-1))

src/arch/mips/utility.cc

@@ -47,7 +47,6 @@ uint64_t
 getArgument(ThreadContext *tc, int &number, uint16_t size, bool fp)
 {
     panic("getArgument() not implemented\n");
-    M5_DUMMY_RETURN
 }
 
 uint64_t

src/arch/sparc/utility.cc

@@ -43,10 +43,7 @@ namespace SparcISA {
 uint64_t
 getArgument(ThreadContext *tc, int &number, uint16_t size, bool fp)
 {
-    if (!FullSystem) {
-        panic("getArgument() only implemented for full system\n");
-        M5_DUMMY_RETURN
-    }
+    panic_if(!FullSystem, "getArgument() only implemented for full system");
 
     const int NumArgumentRegs = 6;
     if (number < NumArgumentRegs) {

src/base/compiler.hh

@@ -47,7 +47,6 @@
 
 #if defined(__GNUC__) // clang or gcc
 #  define M5_ATTR_NORETURN  __attribute__((noreturn))
-#  define M5_DUMMY_RETURN
 #  define M5_VAR_USED __attribute__((unused))
 #  define M5_ATTR_PACKED __attribute__ ((__packed__))
 #  define M5_NO_INLINE __attribute__ ((__noinline__))

src/cpu/static_inst.cc

@@ -106,7 +106,6 @@ StaticInst::branchTarget(const TheISA::PCState &pc) const
 {
     panic("StaticInst::branchTarget() called on instruction "
           "that is not a PC-relative branch.");
-    M5_DUMMY_RETURN;
 }
 
 TheISA::PCState
@@ -114,7 +113,6 @@ StaticInst::branchTarget(ThreadContext *tc) const
 {
     panic("StaticInst::branchTarget() called on instruction "
           "that is not an indirect branch.");
-    M5_DUMMY_RETURN;
 }
 
 const string &

src/dev/baddev.cc

@@ -49,14 +49,12 @@ Tick
 BadDevice::read(PacketPtr pkt)
 {
     panic("Device %s not imlpmented\n", devname);
-    M5_DUMMY_RETURN
 }
 
 Tick
 BadDevice::write(PacketPtr pkt)
 {
     panic("Device %s not imlpmented\n", devname);
-    M5_DUMMY_RETURN
 }
 
 BadDevice *

src/dev/mips/malta.hh

@@ -108,21 +108,18 @@ class Malta : public Platform
     calcPciConfigAddr(int bus, int dev, int func)
     {
         panic("Need implementation\n");
-        M5_DUMMY_RETURN
     }
 
     Addr
     calcPciIOAddr(Addr addr)
     {
         panic("Need implementation\n");
-        M5_DUMMY_RETURN
     }
 
     Addr
     calcPciMemAddr(Addr addr)
     {
         panic("Need implementation\n");
-        M5_DUMMY_RETURN
     }
 
     void serialize(CheckpointOut &cp) const override;

src/dev/sparc/t1000.cc

@@ -75,7 +75,6 @@ Addr
 T1000::pciToDma(Addr pciAddr) const
 {
     panic("Need implementation\n");
-    M5_DUMMY_RETURN
 }
 
 
@@ -83,21 +82,18 @@ Addr
 T1000::calcPciConfigAddr(int bus, int dev, int func)
 {
     panic("Need implementation\n");
-    M5_DUMMY_RETURN
 }
 
 Addr
 T1000::calcPciIOAddr(Addr addr)
 {
     panic("Need implementation\n");
-    M5_DUMMY_RETURN
 }
 
 Addr
 T1000::calcPciMemAddr(Addr addr)
 {
     panic("Need implementation\n");
-    M5_DUMMY_RETURN
 }
 
 T1000 *