[llvm] r302704 - [APInt] Make toString use udivrem instead of calling the divide helper method directly. Do a better job of reusing allocations while looping. NFCI

[Craig Topper via llvm-commits]

Author: ctopper
Date: Wed May 10 13:15:24 2017
New Revision: 302704

URL: http://llvm.org/viewvc/llvm-project?rev=302704&view=rev
Log:
[APInt] Make toString use udivrem instead of calling the divide helper method directly. Do a better job of reusing allocations while looping. NFCI

This lets toString take advantage of the degenerate case checks in udivrem and is just generally cleaner.

One minor downside of this is that the divisor APInt now needs to be the same size as Tmp which requires an additional allocation. But we were doing a poor job of reusing allocations before so the new code should still be an improvement.

Modified:
    llvm/trunk/lib/Support/APInt.cpp

Modified: llvm/trunk/lib/Support/APInt.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/APInt.cpp?rev=302704&r1=302703&r2=302704&view=diff
==============================================================================
--- llvm/trunk/lib/Support/APInt.cpp (original)
+++ llvm/trunk/lib/Support/APInt.cpp Wed May 10 13:15:24 2017
@@ -1948,22 +1948,23 @@ void APInt::toString(SmallVectorImpl<cha
     unsigned ShiftAmt = (Radix == 16 ? 4 : (Radix == 8 ? 3 : 1));
     unsigned MaskAmt = Radix - 1;
 
-    while (Tmp != 0) {
+    while (Tmp.getBoolValue()) {
       unsigned Digit = unsigned(Tmp.getRawData()[0]) & MaskAmt;
       Str.push_back(Digits[Digit]);
       Tmp.lshrInPlace(ShiftAmt);
     }
   } else {
-    APInt divisor(Radix == 10? 4 : 8, Radix);
-    while (Tmp != 0) {
-      APInt APdigit(1, 0);
-      APInt tmp2(Tmp.getBitWidth(), 0);
-      divide(Tmp, Tmp.getNumWords(), divisor, divisor.getNumWords(), &tmp2,
-             &APdigit);
+    APInt divisor(Tmp.getBitWidth(), Radix);
+    APInt APdigit;
+    APInt tmp2(Tmp.getBitWidth(), 0);
+    while (Tmp.getBoolValue()) {
+      udivrem(Tmp, divisor, tmp2, APdigit);
       unsigned Digit = (unsigned)APdigit.getZExtValue();
       assert(Digit < Radix && "divide failed");
       Str.push_back(Digits[Digit]);
-      Tmp = tmp2;
+      // Move the quotient into Tmp and move the old allocation of Tmp into
+      // tmp2 to be used on the next loop iteration.
+      std::swap(Tmp, tmp2);
     }
   }