[PATCH] Fix bug causing loop unrolling to be disabled in some cases for loops with '#pragma clang loop unroll_count(N)"

[Mark Heffernan]

Hi hfinkel,

After unrolling a loop with llvm.loop.unroll.count metadata (unroll factor hint) the loop unroller replaces the llvm.loop.unroll.count metadata with llvm.loop.unroll.disable metadata to prevent any subsequent unrolling passes from unrolling more than the hint indicates.  However, if the unroll count metadata is shared between loops then unrolling for these other loops will also be disabled.  This small patch fixes that problem by adding the llvm.loop.unroll.disable metadata to only the loop which was just unrolled.

http://reviews.llvm.org/D4662

Files:
  lib/Transforms/Scalar/LoopUnrollPass.cpp

Index: lib/Transforms/Scalar/LoopUnrollPass.cpp
===================================================================
--- lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -302,7 +302,6 @@
   // Set operand 0 to refer to the loop id itself.
   NewLoopID->replaceOperandWith(0, NewLoopID);
   L->setLoopID(NewLoopID);
-  LoopID->replaceAllUsesWith(NewLoopID);
 }
 
 unsigned LoopUnroll::selectUnrollCount(
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