Get rid of the getPointeeAlignment helper function from

InstCombineLoadStoreAlloca.cpp, which had many issues.
(At least two bugs were noted on llvm-commits, and it was overly conservative.)
Instead, use getOrEnforceKnownAlignment.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168629 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 14 insertions, 22 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 4d106fc188..fd684200fc 100644
--- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -150,26 +150,6 @@ isOnlyCopiedFromConstantGlobal(AllocaInst *AI,
   return 0;
 }
 
-/// getPointeeAlignment - Compute the minimum alignment of the value pointed
-/// to by the given pointer.
-static unsigned getPointeeAlignment(Value *V, const DataLayout &TD) {
-  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
-    if (CE->getOpcode() == Instruction::BitCast ||
-        (CE->getOpcode() == Instruction::GetElementPtr &&
-         cast<GEPOperator>(CE)->hasAllZeroIndices()))
-      return getPointeeAlignment(CE->getOperand(0), TD);
-
-  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
-    if (!GV->isDeclaration())
-      return TD.getPreferredAlignment(GV);
-
-  if (PointerType *PT = dyn_cast<PointerType>(V->getType()))
-    if (PT->getElementType()->isSized())
-      return TD.getABITypeAlignment(PT->getElementType());
-
-  return 0;
-}
-
 Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
   // Ensure that the alloca array size argument has type intptr_t, so that
   // any casting is exposed early.
@@ -265,7 +245,7 @@ Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
     }
   }
 
-  if (TD) {
+  if (AI.getAlignment()) {
     // Check to see if this allocation is only modified by a memcpy/memmove from
     // a constant global whose alignment is equal to or exceeds that of the
     // allocation.  If this is the case, we can change all users to use
@@ -274,7 +254,9 @@ Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
     // is only subsequently read.
     SmallVector<Instruction *, 4> ToDelete;
     if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(&AI, ToDelete)) {
-      if (AI.getAlignment() <= getPointeeAlignment(Copy->getSource(), *TD)) {
+      unsigned SourceAlign = getOrEnforceKnownAlignment(Copy->getSource(),
+                                                        AI.getAlignment(), TD);
+      if (AI.getAlignment() <= SourceAlign) {
         DEBUG(dbgs() << "Found alloca equal to global: " << AI << '\n');
         DEBUG(dbgs() << "  memcpy = " << *Copy << '\n');
         for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)
diff --git a/test/Transforms/InstCombine/memcpy-from-global.ll b/test/Transforms/InstCombine/memcpy-from-global.ll
index 83c893e17d..557b160a87 100644
--- a/test/Transforms/InstCombine/memcpy-from-global.ll
+++ b/test/Transforms/InstCombine/memcpy-from-global.ll
@@ -134,3 +134,13 @@ define void @test8() {
 ; CHECK: bar
   ret void
 }
+
+define void @test9() {
+  %A = alloca %U, align 4
+  %a = bitcast %U* %A to i8*
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a, i8* bitcast (%U* getelementptr ([2 x %U]* @H, i64 0, i32 1) to i8*), i64 20, i32 4, i1 false)
+  call void @bar(i8* %a) readonly
+; CHECK: @test9
+; CHECK-NEXT: call void @bar(i8* bitcast (%U* getelementptr inbounds ([2 x %U]* @H, i64 0, i64 1) to i8*))
+  ret void
+}