GodeGen, NFC: Add test to track emitStoresForConstant behavior

[vitalybuka]

format

[vitalybuka]

add test

[eugenis]

LGTM

clang/test/CodeGen/init-memset.c

37

Would it be useful to check the range of the memset? I.e. does it overlap with the following store or not.

[vitalybuka]

clang/test/CodeGen/init-memset.c

37

I don't change ranges to it will only complicate tests

clang/lib/CodeGen/CGDecl.cpp

static llvm::Value *shouldUseMemSetToInitialize(CodeGenModule &CGM,
   }
 
   // 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))
+  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

+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -O0 -emit-llvm -o - %s | FileCheck %s
+
+void use(void *);
+
+void test_small() {
+  // CHECK-LABEL: define void @test_small()
+  int a[] = {1, 2, 3, 4};
+  // CHECK: call void @llvm.memcpy.{{.*}}
+  use(a);
+}
+
+void test_differen() {
+  // CHECK-LABEL: define void @test_differen()
+  int a[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
+  // CHECK: call void @llvm.memcpy.{{.*}}
+  use(a);
+}
+
+void test_all_zeros() {
+  // CHECK-LABEL: define 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.{{.*}}
+  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.{{.*}}
+  use(a);
+}