CodeGen: Use memset in initializers for non-zeros

[hfinkel]

clang/test/CodeGen/init-memset.c

29

I'd be more comfortable if the test here actually checked the length and the value in the memset call here and below.

clang/lib/CodeGen/CGDecl.cpp

if (0) {
     }
   }
 
   // TODO: Tweak these constants or use "density".
   uint64_t SizeLimit = 32;
   if (GlobalSize <= SizeLimit)
     return nullptr;
 
-  // TODO: Remove. It's here just to keep behavior.
-  if (MFB.Other && MFB.Value &&
-      MFB.Value != llvm::ConstantInt::get(CGM.Int8Ty, 0))
-    return nullptr;
-
   if (!MFB.Value) {
     // We don't know most frequent byte, we may still completely initialize it
     // with small number of stores.
     // TODO: Use llvm::UndefValue::get. If we get here and later we decide
     // that number of stores is small enough to use memset+store then store are
     // going to replace entire bzeroed range. With UndefValue we can skip that
     // bogus memset. I will do that as a separate patch.
     MFB.Value = llvm::ConstantInt::get(CGM.Int8Ty, 0);

clang/test/CodeGen/init-memset.c

void test_all_zeros() {
   int a[16] = {};
   // CHECK: call void @llvm.memset.{{.*}}
   use(a);
 }
 
 void test_all_a() {
   // CHECK-LABEL: define void @test_all_a()
   char a[] = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
-  // CHECK: call void @llvm.memcpy.{{.*}}
+  // CHECK: call void @llvm.memset.{{.*}}
   use(a);
 }
 
 void test_most_zeros() {
   // CHECK-LABEL: define void @test_most_zeros()
   int a[16] = {0, 0, 1};
   // CHECK: call void @llvm.memset.{{.*}}
   // CHECK: store i32 1
   use(a);
 }
 
 void test_most_a() {
   // CHECK-LABEL: define void @test_most_a()
   char a[] = "aaaaazaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
-  // CHECK: call void @llvm.memcpy.{{.*}}
+  // CHECK: call void @llvm.memset.{{.*}}
+  // CHECK: store i8 122
   use(a);
 }