When the inliner merges allocas, it must keep the larger alignment

For safety, the inliner cannot decrease the allignment on an alloca when
merging it with another.

I've included two variants of the test case for this: one with DataLayout
available, and one without. When DataLayout is not available, if only one of
the allocas uses the default alignment (getAlignment() == 0), then they cannot
be safely merged.

llvm-svn: 186425

1 files changed, 16 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/IPO/Inliner.cpp b/llvm/lib/Transforms/IPO/Inliner.cpp
index 663ddb75f42..f72121d822f 100644
--- a/llvm/lib/Transforms/IPO/Inliner.cpp
+++ b/llvm/lib/Transforms/IPO/Inliner.cpp
@@ -116,7 +116,8 @@ static void AdjustCallerSSPLevel(Function *Caller, Function *Callee) {
 /// any new allocas to the set if not possible.
 static bool InlineCallIfPossible(CallSite CS, InlineFunctionInfo &IFI,
                                  InlinedArrayAllocasTy &InlinedArrayAllocas,
-                                 int InlineHistory, bool InsertLifetime) {
+                                 int InlineHistory, bool InsertLifetime,
+                                 const DataLayout *TD) {
   Function *Callee = CS.getCalledFunction();
   Function *Caller = CS.getCaller();
 
@@ -189,6 +190,14 @@ static bool InlineCallIfPossible(CallSite CS, InlineFunctionInfo &IFI,
     bool MergedAwayAlloca = false;
     for (unsigned i = 0, e = AllocasForType.size(); i != e; ++i) {
       AllocaInst *AvailableAlloca = AllocasForType[i];
+
+      unsigned Align1 = AI->getAlignment(),
+               Align2 = AvailableAlloca->getAlignment();
+      // If we don't have data layout information, and only one alloca is using
+      // the target default, then we can't safely merge them because we can't
+      // pick the greater alignment.
+      if (!TD && (!Align1 || !Align2) && Align1 != Align2)
+        continue;
       
       // The available alloca has to be in the right function, not in some other
       // function in this SCC.
@@ -206,6 +215,11 @@ static bool InlineCallIfPossible(CallSite CS, InlineFunctionInfo &IFI,
                    << *AvailableAlloca << '\n');
       
       AI->replaceAllUsesWith(AvailableAlloca);
+
+      if (Align1 > Align2 || (!Align1 && TD &&
+          TD->getABITypeAlignment(AI->getAllocatedType()) > Align2))
+        AvailableAlloca->setAlignment(Align1);
+
       AI->eraseFromParent();
       MergedAwayAlloca = true;
       ++NumMergedAllocas;
@@ -482,7 +496,7 @@ bool Inliner::runOnSCC(CallGraphSCC &SCC) {
 
         // Attempt to inline the function.
         if (!InlineCallIfPossible(CS, InlineInfo, InlinedArrayAllocas,
-                                  InlineHistoryID, InsertLifetime))
+                                  InlineHistoryID, InsertLifetime, TD))
           continue;
         ++NumInlined;