[patch] fix comment on findGCD

[Mingjie Xing]

Hi,

While reading source code again, I think it is not a simple comment
typo. The function
findGCD always finds the GCD. So the boolean return value depends on the meaning
what we want it to be. We say the Diophantine equation has a solution
iff GCD divides
Delta. And the dependence is disproved if there is no solution.

So if we want findGCD return true when GCD divides Delta, souce code
should be fixed
as the following patch,

Index: lib/Analysis/DependenceAnalysis.cpp
===================================================================
--- lib/Analysis/DependenceAnalysis.cpp (revision 198188)
+++ lib/Analysis/DependenceAnalysis.cpp (working copy)
@@ -1275,7 +1275,7 @@
 //
 // Program 2.1, page 29.
 // Computes the GCD of AM and BM.
-// Also finds a solution to the equation ax - by = gdc(a, b).
+// Also finds a solution to the equation ax - by = gcd(a, b).
 // Returns true iff the gcd divides Delta.
 static
 bool findGCD(unsigned Bits, APInt AM, APInt BM, APInt Delta,
@@ -1301,11 +1301,11 @@
   // make sure gcd divides Delta
   R = Delta.srem(G);
   if (R != 0)
-    return true; // gcd doesn't divide Delta, no dependence
+    return false; // gcd doesn't divide Delta, no dependence
   Q = Delta.sdiv(G);
   X *= Q;
   Y *= Q;
-  return false;
+  return true;
 }


@@ -1398,7 +1398,7 @@
   APInt AM = ConstSrcCoeff->getValue()->getValue();
   APInt BM = ConstDstCoeff->getValue()->getValue();
   unsigned Bits = AM.getBitWidth();
-  if (findGCD(Bits, AM, BM, ConstDelta->getValue()->getValue(), G, X, Y)) {
+  if (!findGCD(Bits, AM, BM, ConstDelta->getValue()->getValue(), G, X, Y)) {
     // gcd doesn't divide Delta, no dependence
     ++ExactSIVindependence;
     ++ExactSIVsuccesses;
@@ -1802,7 +1802,7 @@
   APInt AM = ConstSrcCoeff->getValue()->getValue();
   APInt BM = ConstDstCoeff->getValue()->getValue();
   unsigned Bits = AM.getBitWidth();
-  if (findGCD(Bits, AM, BM, ConstDelta->getValue()->getValue(), G, X, Y)) {
+  if (!findGCD(Bits, AM, BM, ConstDelta->getValue()->getValue(), G, X, Y)) {
     // gcd doesn't divide Delta, no dependence
     ++ExactRDIVindependence;
     return true;

Best Regards,
Mingjie