Fix a nasty bug that caused us to unroll EXTREMELY large loops due to overflow

in the size calculation.

This is not something you want to see:
Loop Unroll: F[main] Loop %no_exit Loop Size = 2 Trip Count = 2147483648 - UNROLLING!

The problem was that 2*2147483648 == 0.

Now we get:
Loop Unroll: F[main] Loop %no_exit Loop Size = 2 Trip Count = 2147483648 - TOO LARGE: 4294967296>100

Thanks to some anonymous person playing with the demo page that repeatedly
caused zion to go into swapping land.  That's one way to ensure you'll get
a quick bugfix.  :)

Testcase here: Transforms/LoopUnroll/2004-05-13-DontUnrollTooMuch.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13564 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/Transforms/Scalar/LoopUnroll.cpp b/lib/Transforms/Scalar/LoopUnroll.cpp
index 33148200b4..a9cced5ce1 100644
--- a/lib/Transforms/Scalar/LoopUnroll.cpp
+++ b/lib/Transforms/Scalar/LoopUnroll.cpp
@@ -139,9 +139,9 @@ bool LoopUnroll::visitLoop(Loop *L) {
   DEBUG(std::cerr << "Loop Unroll: F[" << BB->getParent()->getName()
         << "] Loop %" << BB->getName() << " Loop Size = " << LoopSize
         << " Trip Count = " << TripCount << " - ");
-  if (LoopSize*TripCount > UnrollThreshold) {
-    DEBUG(std::cerr << "TOO LARGE: " << LoopSize*TripCount << ">"
-                    << UnrollThreshold << "\n");
+  uint64_t Size = (uint64_t)LoopSize*(uint64_t)TripCount;
+  if (Size > UnrollThreshold) {
+    DEBUG(std::cerr << "TOO LARGE: " << Size << ">" << UnrollThreshold << "\n");
     return Changed;
   }
   DEBUG(std::cerr << "UNROLLING!\n");