Fix misleading comment for getOrEnforceKnownAlignment

It does not return 0 to indicate failure, and returns the known
alignment.

llvm-svn: 281350

2 files changed, 9 insertions, 8 deletions

diff --git a/llvm/include/llvm/Transforms/Utils/Local.h b/llvm/include/llvm/Transforms/Utils/Local.h
index b6f9e7f5735..9267b10c0ab 100644
--- a/llvm/include/llvm/Transforms/Utils/Local.h
+++ b/llvm/include/llvm/Transforms/Utils/Local.h
@@ -161,10 +161,15 @@ AllocaInst *DemoteRegToStack(Instruction &X,
 /// deleted and it returns the pointer to the alloca inserted.
 AllocaInst *DemotePHIToStack(PHINode *P, Instruction *AllocaPoint = nullptr);
 
-/// If the specified pointer has an alignment that we can determine, return it,
-/// otherwise return 0. If PrefAlign is specified, and it is more than the
-/// alignment of the ultimate object, see if we can increase the alignment of
-/// the ultimate object, making this check succeed.
+/// Try to ensure that the alignment of \p V is at least \p PrefAlign bytes. If
+/// the owning object can be modified and has an alignment less than \p
+/// PrefAlign, it will be increased and \p PrefAlign returned. If the alignment
+/// cannot be increased, the known alignment of the value is returned.
+///
+/// It is not always possible to modify the alignment of the underlying object,
+/// so if alignment is important, a more reliable approach is to simply align
+/// all global variables and allocation instructions to their preferred
+/// alignment from the beginning.
 unsigned getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
                                     const DataLayout &DL,
                                     const Instruction *CxtI = nullptr,
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 87524e660f0..c1ef655be4b 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1001,10 +1001,6 @@ static unsigned enforceKnownAlignment(Value *V, unsigned Align,
   return Align;
 }
 
-/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
-/// we can determine, return it, otherwise return 0.  If PrefAlign is specified,
-/// and it is more than the alignment of the ultimate object, see if we can
-/// increase the alignment of the ultimate object, making this check succeed.
 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
                                           const DataLayout &DL,
                                           const Instruction *CxtI,