Stores of null pointers should turn into memset, we weren't recognizing

them as splat values.

llvm-svn: 126041

2 files changed, 27 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 32d2c887211..1060bc5349e 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1163,6 +1163,11 @@ bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
 Value *llvm::isBytewiseValue(Value *V) {
   // All byte-wide stores are splatable, even of arbitrary variables.
   if (V->getType()->isIntegerTy(8)) return V;
+
+  // Handle 'null' ConstantArrayZero etc.
+  if (Constant *C = dyn_cast<Constant>(V))
+    if (C->isNullValue())
+      return Constant::getNullValue(Type::getInt8Ty(V->getContext()));
   
   // Constant float and double values can be handled as integer values if the
   // corresponding integer value is "byteable".  An important case is 0.0. 
diff --git a/llvm/test/Transforms/LoopIdiom/basic.ll b/llvm/test/Transforms/LoopIdiom/basic.ll
index ead2e6f11cd..122d25a22a0 100644
--- a/llvm/test/Transforms/LoopIdiom/basic.ll
+++ b/llvm/test/Transforms/LoopIdiom/basic.ll
@@ -299,4 +299,26 @@ for.end:                                          ; preds = %for.body
 ; CHECK: ret void
 }
 
+; Store of null should turn into memset of zero.
+define void @test12(i32** nocapture %P) nounwind ssp {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  %indvar = phi i64 [ 0, %entry ], [ %indvar.next, %for.body ]
+  %arrayidx = getelementptr i32** %P, i64 %indvar
+  store i32* null, i32** %arrayidx, align 4
+  %indvar.next = add i64 %indvar, 1
+  %exitcond = icmp eq i64 %indvar.next, 10000
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  ret void
+; CHECK: @test12
+; CHECK-NEXT: entry:
+; CHECK-NEXT: bitcast
+; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* %P1, i8 0, i64 80000, i32 4, i1 false)
+; CHECK-NOT: store
+; CHECK: ret void
+}