Remove my `scalar_copy_backend_type` optimization attempt

I added this back in 111999, but I no longer think it's a good idea
- It had to get scaled back to only power-of-two things to not break a bunch of targets
- LLVM seems to be getting better at memcpy removal anyway
- Introducing vector instructions has seemed to sometimes (115515) make autovectorization worse

So this removes it from the codegen crates entirely, and instead just tries to use <https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/traits/builder/trait.BuilderMethods.html#method.typed_place_copy> instead of direct `memcpy` so things will still use load/store for immediates.

3 files changed, 31 insertions, 27 deletions

diff --git a/tests/codegen/array-codegen.rs b/tests/codegen/array-codegen.rs
index bb4bd5444db..1310e61c41d 100644
--- a/tests/codegen/array-codegen.rs
+++ b/tests/codegen/array-codegen.rs
@@ -5,52 +5,58 @@
 // CHECK-LABEL: @array_load
 #[no_mangle]
 pub fn array_load(a: &[u8; 4]) -> [u8; 4] {
-    // CHECK: %_0 = alloca [4 x i8], align 1
-    // CHECK: %[[TEMP1:.+]] = load <4 x i8>, ptr %a, align 1
-    // CHECK: store <4 x i8> %[[TEMP1]], ptr %_0, align 1
-    // CHECK: %[[TEMP2:.+]] = load i32, ptr %_0, align 1
-    // CHECK: ret i32 %[[TEMP2]]
+    // CHECK-NOT: alloca
+    // CHECK: %[[ALLOCA:.+]] = alloca [4 x i8], align 1
+    // CHECK-NOT: alloca
+    // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 1 %[[ALLOCA]], ptr align 1 %a, {{.+}} 4, i1 false)
+    // CHECK: %[[TEMP:.+]] = load i32, ptr %[[ALLOCA]], align 1
+    // CHECK: ret i32 %[[TEMP]]
     *a
 }
 
 // CHECK-LABEL: @array_store
 #[no_mangle]
 pub fn array_store(a: [u8; 4], p: &mut [u8; 4]) {
+    // CHECK-NOT: alloca
+    // CHECK: %[[TEMP:.+]] = alloca i32, [[TEMPALIGN:align [0-9]+]]
+    // CHECK-NOT: alloca
     // CHECK: %a = alloca [4 x i8]
-    // CHECK: %[[TEMP:.+]] = load <4 x i8>, ptr %a, align 1
-    // CHECK-NEXT: store <4 x i8> %[[TEMP]], ptr %p, align 1
+    // CHECK-NOT: alloca
+    // store i32 %0, ptr %[[TEMP]]
+    // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 1 %a, ptr [[TEMPALIGN]] %[[TEMP]], {{.+}} 4, i1 false)
+    // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 1 %p, ptr align 1 %a, {{.+}} 4, i1 false)
     *p = a;
 }
 
 // CHECK-LABEL: @array_copy
 #[no_mangle]
 pub fn array_copy(a: &[u8; 4], p: &mut [u8; 4]) {
+    // CHECK-NOT: alloca
     // CHECK: %[[LOCAL:.+]] = alloca [4 x i8], align 1
-    // CHECK: %[[TEMP1:.+]] = load <4 x i8>, ptr %a, align 1
-    // CHECK: store <4 x i8> %[[TEMP1]], ptr %[[LOCAL]], align 1
-    // CHECK: %[[TEMP2:.+]] = load <4 x i8>, ptr %[[LOCAL]], align 1
-    // CHECK: store <4 x i8> %[[TEMP2]], ptr %p, align 1
+    // CHECK-NOT: alloca
+    // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 1 %[[LOCAL]], ptr align 1 %a, {{.+}} 4, i1 false)
+    // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 1 %p, ptr align 1 %[[LOCAL]], {{.+}} 4, i1 false)
     *p = *a;
 }
 
 // CHECK-LABEL: @array_copy_1_element
 #[no_mangle]
 pub fn array_copy_1_element(a: &[u8; 1], p: &mut [u8; 1]) {
+    // CHECK-NOT: alloca
     // CHECK: %[[LOCAL:.+]] = alloca [1 x i8], align 1
-    // CHECK: %[[TEMP1:.+]] = load i8, ptr %a, align 1
-    // CHECK: store i8 %[[TEMP1]], ptr %[[LOCAL]], align 1
-    // CHECK: %[[TEMP2:.+]] = load i8, ptr %[[LOCAL]], align 1
-    // CHECK: store i8 %[[TEMP2]], ptr %p, align 1
+    // CHECK-NOT: alloca
+    // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 1 %[[LOCAL]], ptr align 1 %a, {{.+}} 1, i1 false)
+    // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 1 %p, ptr align 1 %[[LOCAL]], {{.+}} 1, i1 false)
     *p = *a;
 }
 
 // CHECK-LABEL: @array_copy_2_elements
 #[no_mangle]
 pub fn array_copy_2_elements(a: &[u8; 2], p: &mut [u8; 2]) {
+    // CHECK-NOT: alloca
     // CHECK: %[[LOCAL:.+]] = alloca [2 x i8], align 1
-    // CHECK: %[[TEMP1:.+]] = load <2 x i8>, ptr %a, align 1
-    // CHECK: store <2 x i8> %[[TEMP1]], ptr %[[LOCAL]], align 1
-    // CHECK: %[[TEMP2:.+]] = load <2 x i8>, ptr %[[LOCAL]], align 1
-    // CHECK: store <2 x i8> %[[TEMP2]], ptr %p, align 1
+    // CHECK-NOT: alloca
+    // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 1 %[[LOCAL]], ptr align 1 %a, {{.+}} 2, i1 false)
+    // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 1 %p, ptr align 1 %[[LOCAL]], {{.+}} 2, i1 false)
     *p = *a;
 }
diff --git a/tests/codegen/array-optimized.rs b/tests/codegen/array-optimized.rs
index 4cf16f1fb30..42fdbd39b7e 100644
--- a/tests/codegen/array-optimized.rs
+++ b/tests/codegen/array-optimized.rs
@@ -16,8 +16,8 @@ pub fn array_copy_1_element(a: &[u8; 1], p: &mut [u8; 1]) {
 #[no_mangle]
 pub fn array_copy_2_elements(a: &[u8; 2], p: &mut [u8; 2]) {
     // CHECK-NOT: alloca
-    // CHECK: %[[TEMP:.+]] = load <2 x i8>, ptr %a, align 1
-    // CHECK: store <2 x i8> %[[TEMP]], ptr %p, align 1
+    // CHECK: %[[TEMP:.+]] = load i16, ptr %a, align 1
+    // CHECK: store i16 %[[TEMP]], ptr %p, align 1
     // CHECK: ret
     *p = *a;
 }
@@ -26,8 +26,8 @@ pub fn array_copy_2_elements(a: &[u8; 2], p: &mut [u8; 2]) {
 #[no_mangle]
 pub fn array_copy_4_elements(a: &[u8; 4], p: &mut [u8; 4]) {
     // CHECK-NOT: alloca
-    // CHECK: %[[TEMP:.+]] = load <4 x i8>, ptr %a, align 1
-    // CHECK: store <4 x i8> %[[TEMP]], ptr %p, align 1
+    // CHECK: %[[TEMP:.+]] = load i32, ptr %a, align 1
+    // CHECK: store i32 %[[TEMP]], ptr %p, align 1
     // CHECK: ret
     *p = *a;
 }
diff --git a/tests/codegen/mem-replace-simple-type.rs b/tests/codegen/mem-replace-simple-type.rs
index b00fbad05d9..50b43f5854a 100644
--- a/tests/codegen/mem-replace-simple-type.rs
+++ b/tests/codegen/mem-replace-simple-type.rs
@@ -45,9 +45,7 @@ pub fn replace_short_array_3(r: &mut [u32; 3], v: [u32; 3]) -> [u32; 3] {
 // CHECK-LABEL: @replace_short_array_4(
 pub fn replace_short_array_4(r: &mut [u32; 4], v: [u32; 4]) -> [u32; 4] {
     // CHECK-NOT: alloca
-    // CHECK: %[[R:.+]] = load <4 x i32>, ptr %r, align 4
-    // CHECK: store <4 x i32> %[[R]], ptr %result
-    // CHECK: %[[V:.+]] = load <4 x i32>, ptr %v, align 4
-    // CHECK: store <4 x i32> %[[V]], ptr %r
+    // CHECK: call void @llvm.memcpy.p0.p0.i64(ptr align 4 %result, ptr align 4 %r, i64 16, i1 false)
+    // CHECK: call void @llvm.memcpy.p0.p0.i64(ptr align 4 %r, ptr align 4 %v, i64 16, i1 false)
     std::mem::replace(r, v)
 }