[APInt] Don't print debug messages from the APInt knuth division algorithm by default

[craig.topper]

Summary

Debug builds currently print out low level details of the Knuth division algorithm when -debug is used. This information isn't useful in most cases and just adds noise to the log.

This adds a new preprocessor flag to enable the prints in the knuth division code in APInt.

[majnemer]

LGTM, this had bugged me too.

[majnemer]

lib/Support/APInt.cpp

1255–1259 ↗

(On Diff #124114)

*might* be nicer to use push_macro/pop_macro? Up to you in any case.

llvm/trunk/lib/Support/APInt.cpp

static void KnuthDiv(uint32_t *u, uint32_t *v, uint32_t *q, uint32_t* r,
   assert(v && "Must provide divisor");
   assert(q && "Must provide quotient");
   assert(u != v && u != q && v != q && "Must use different memory");
   assert(n>1 && "n must be > 1");
 
   // b denotes the base of the number system. In our case b is 2^32.
   const uint64_t b = uint64_t(1) << 32;
 
+// The DEBUG macros here tend to be spam in the debug output if you're not
+// debugging this code. Disable them unless KNUTH_DEBUG is defined.
+#pragma push_macro("DEBUG")
+#ifndef KNUTH_DEBUG
+#undef DEBUG
+#define DEBUG(X) do {} while (true)
+#endif
+
   DEBUG(dbgs() << "KnuthDiv: m=" << m << " n=" << n << '\n');
   DEBUG(dbgs() << "KnuthDiv: original:");
   DEBUG(for (int i = m+n; i >=0; i--) dbgs() << " " << u[i]);
   DEBUG(dbgs() << " by");
   DEBUG(for (int i = n; i >0; i--) dbgs() << " " << v[i-1]);
   DEBUG(dbgs() << '\n');
   // D1. [Normalize.] Set d = b / (v[n-1] + 1) and multiply all the digits of
   // u and v by d. Note that we have taken Knuth's advice here to use a power
if (shift) {
       for (int i = n-1; i >= 0; i--) {
         r[i] = u[i];
         DEBUG(dbgs() << " " << r[i]);
       }
     }
     DEBUG(dbgs() << '\n');
   }
   DEBUG(dbgs() << '\n');
+
+#pragma pop_macro("DEBUG")
 }
 
 void APInt::divide(const WordType *LHS, unsigned lhsWords, const WordType *RHS,
                    unsigned rhsWords, WordType *Quotient, WordType *Remainder) {
   assert(lhsWords >= rhsWords && "Fractional result");
 
   // First, compose the values into an array of 32-bit words instead of
   // 64-bit words. This is a necessity of both the "short division" algorithm