arch-arm,base,dev: Eliminate the power() function from intmath.hh.

This function causes problems with gcc 5 which incorrectly complains
about the call to warn_if inside a constexpr function. That should only
be an error if a call to a non-constexpr is unavoidable, and even then
the compiler isn't required to emit a diagnostic.

Rather than drop the warning, or add ifdefs to deal with these defective
versions of gcc, this change eliminates the power() function entirely.
Most inputs to this function would overflow anyway, which is reportedly
why no integer version of an exponentiation function is defined in the
standard library, and all uses of this function can easily and more
efficiently be replaced by simple left and right shifts.

Finally, by eliminating the power() function, we also remove the
dependence on base/logging.hh.

Change-Id: I4d014163883d12db46da4ee752696c8225534ee8
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42504
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/arm/isa/insts/data64.isa

@@ -382,7 +382,7 @@ let {{
            Request::Flags memAccessFlags = Request::CACHE_BLOCK_ZERO;
            EA = XBase;
            assert(!(Dczid & 0x10));
-           uint64_t op_size = power(2, Dczid + 2);
+           uint64_t op_size = 1ULL << (Dczid + 2);
            EA &= ~(op_size - 1);
 
    '''

src/base/intmath.hh

@@ -46,28 +46,8 @@
 #include <type_traits>
 
 #include "base/bitfield.hh"
-#include "base/logging.hh"
 #include "base/types.hh"
 
-/**
- * @ingroup api_base_utils
- */
-static constexpr uint64_t
-power(uint32_t n, uint32_t e)
-{
-    uint64_t result = 1;
-    uint64_t component = n;
-    while (e) {
-        uint64_t last = result;
-        if (e & 0x1)
-            result *= component;
-        warn_if(result < last, "power() overflowed!");
-        e >>= 1;
-        component *= component;
-    }
-    return result;
-}
-
 /**
  * @ingroup api_base_utils
  */

src/base/intmath.test.cc

@@ -54,13 +54,6 @@ TEST(IntmathTest, isPowerOf2)
     EXPECT_FALSE(isPowerOf2(1679616));
 }
 
-TEST(IntmathTest, power)
-{
-    EXPECT_EQ(65536, power(2, 16));
-    EXPECT_EQ(9765625, power(5, 10));
-    EXPECT_EQ(43046721, power(power(3, 4), 4));
-}
-
 TEST(IntmathTest, floorLog2)
 {
     EXPECT_EQ(0, floorLog2(1));

src/dev/arm/timer_cpulocal.cc

@@ -123,8 +123,7 @@ CpuLocalTimer::Timer::read(PacketPtr pkt, Addr daddr)
                 timerZeroEvent.when(), parent->clockPeriod(),
                 timerControl.prescalar);
         time = timerZeroEvent.when() - curTick();
-        time = time / parent->clockPeriod() /
-            power(16, timerControl.prescalar);
+        time = (time / parent->clockPeriod()) >> (4 * timerControl.prescalar);
         DPRINTF(Timer, "-- returning counter at %d\n", time);
         pkt->setLE<uint32_t>(time);
         break;
@@ -143,8 +142,8 @@ CpuLocalTimer::Timer::read(PacketPtr pkt, Addr daddr)
                 watchdogZeroEvent.when(), parent->clockPeriod(),
                 watchdogControl.prescalar);
         time = watchdogZeroEvent.when() - curTick();
-        time = time / parent->clockPeriod() /
-            power(16, watchdogControl.prescalar);
+        time = (time / parent->clockPeriod()) >>
+            (4 * watchdogControl.prescalar);
         DPRINTF(Timer, "-- returning counter at %d\n", time);
         pkt->setLE<uint32_t>(time);
         break;
@@ -269,7 +268,7 @@ CpuLocalTimer::Timer::restartTimerCounter(uint32_t val)
     if (!timerControl.enable)
         return;
 
-    Tick time = parent->clockPeriod() * power(16, timerControl.prescalar);
+    Tick time = parent->clockPeriod() << (4 * timerControl.prescalar);
     time *= val;
 
     if (timerZeroEvent.scheduled()) {
@@ -287,7 +286,7 @@ CpuLocalTimer::Timer::restartWatchdogCounter(uint32_t val)
     if (!watchdogControl.enable)
         return;
 
-    Tick time = parent->clockPeriod() * power(16, watchdogControl.prescalar);
+    Tick time = parent->clockPeriod() << (4 * watchdogControl.prescalar);
     time *= val;
 
     if (watchdogZeroEvent.scheduled()) {

src/dev/arm/timer_sp804.cc

@@ -96,7 +96,7 @@ Sp804::Timer::read(PacketPtr pkt, Addr daddr)
                 zeroEvent.when(), clock, control.timerPrescale);
         Tick time;
         time = zeroEvent.when() - curTick();
-        time = time / clock / power(16, control.timerPrescale);
+        time = (time / clock) >> (4 * control.timerPrescale);
         DPRINTF(Timer, "-- returning counter at %d\n", time);
         pkt->setLE<uint32_t>(time);
         break;
@@ -182,7 +182,7 @@ Sp804::Timer::restartCounter(uint32_t val)
     if (!control.timerEnable)
         return;
 
-    Tick time = clock * power(16, control.timerPrescale);
+    Tick time = clock << (4 * control.timerPrescale);
     if (control.timerSize)
         time *= val;
     else