cpu: Merge TimingExprSrcReg and TimingExprReadIntReg.

Make it possible to read any type of reg, assuming it fits in a RegVal.
This avoids assuming building in a dependency on the readIntReg
accessor.

It also avoids setting up a situation where the API could at least
theoretically base the timing expression on the value of *any* int reg,
even ones the instruction does not interact with. The ...ReadIntReg
expression was only ever used with the result of the ...SrcReg
expression, and in my opinion, that's realy the only way it makes sense
to use it. It doesn't seem useful to split that operation into two
parts.

If it actually does make sense (although I doubt this), these operations
can't really be generalized easily since the TimingExpr... classes all
expect to pass around uint64_ts, and a RegId, the *real* value of a
SrcReg index which does not assume a register type, would not fit in
that in the general case.

Change-Id: I253a0a058dc078deeb28ef0babead4c8ffc3b792
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49776
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Gabe Black <gabe.black@gmail.com>

src/cpu/SConscript

@@ -98,9 +98,8 @@ SimObject('BaseCPU.py', sim_objects=['BaseCPU'])
 SimObject('CPUTracers.py', sim_objects=[
     'ExeTracer', 'IntelTrace', 'NativeTrace'])
 SimObject('TimingExpr.py', sim_objects=[
-    'TimingExpr', 'TimingExprLiteral', 'TimingExprSrcReg',
-    'TimingExprReadIntReg', 'TimingExprLet', 'TimingExprRef', 'TimingExprUn',
-    'TimingExprBin', 'TimingExprIf'],
+    'TimingExpr', 'TimingExprLiteral', 'TimingExprSrcReg', 'TimingExprLet',
+    'TimingExprRef', 'TimingExprUn', 'TimingExprBin', 'TimingExprIf'],
     enums=['TimingExprOp'])
 
 Source('activity.cc')

src/cpu/TimingExpr.py

@@ -66,30 +66,17 @@ class TimingExpr0(TimingExprLiteral):
     value = 0
 
 class TimingExprSrcReg(TimingExpr):
-    """Find the source register number from the current inst"""
+    """Read a source register from the current inst"""
     type = 'TimingExprSrcReg'
     cxx_header = 'cpu/timing_expr.hh'
     cxx_class = 'gem5::TimingExprSrcReg'
 
-    # index = Param.Unsigned("index into inst src regs")
-    index = Param.Unsigned("index into inst src regs")
+    index = Param.Unsigned("index into inst src regs of the reg to read")
 
     def set_params(self, index):
         self.index = index
         return self
 
-class TimingExprReadIntReg(TimingExpr):
-    """Read an architectural register"""
-    type = 'TimingExprReadIntReg'
-    cxx_header = 'cpu/timing_expr.hh'
-    cxx_class = 'gem5::TimingExprReadIntReg'
-
-    reg = Param.TimingExpr("register raw index to read")
-
-    def set_params(self, reg):
-        self.reg = reg
-        return self
-
 class TimingExprLet(TimingExpr):
     """Block of declarations"""
     type = 'TimingExprLet'

src/cpu/timing_expr.cc

@@ -59,13 +59,7 @@ TimingExprEvalContext::TimingExprEvalContext(const StaticInstPtr &inst_,
 uint64_t
 TimingExprSrcReg::eval(TimingExprEvalContext &context)
 {
-    return context.inst->srcRegIdx(index).index();
-}
-
-uint64_t
-TimingExprReadIntReg::eval(TimingExprEvalContext &context)
-{
-    return context.thread->readIntReg(reg->eval(context));
+    return context.thread->getReg(context.inst->srcRegIdx(index));
 }
 
 uint64_t

src/cpu/timing_expr.hh

@@ -55,7 +55,6 @@
 #include "params/TimingExprIf.hh"
 #include "params/TimingExprLet.hh"
 #include "params/TimingExprLiteral.hh"
-#include "params/TimingExprReadIntReg.hh"
 #include "params/TimingExprRef.hh"
 #include "params/TimingExprSrcReg.hh"
 #include "params/TimingExprUn.hh"
@@ -124,19 +123,6 @@ class TimingExprSrcReg : public TimingExpr
     uint64_t eval(TimingExprEvalContext &context);
 };
 
-class TimingExprReadIntReg : public TimingExpr
-{
-  public:
-    TimingExpr *reg;
-
-    TimingExprReadIntReg(const TimingExprReadIntRegParams &params) :
-        TimingExpr(params),
-        reg(params.reg)
-    { }
-
-    uint64_t eval(TimingExprEvalContext &context);
-};
-
 class TimingExprLet : public TimingExpr
 {
   public: