[llvm] c9fce5f - X86: adjust the windows 64 calling convention for Swift

[Saleem Abdulrasool via llvm-commits]

Author: Saleem Abdulrasool
Date: 2021-03-13T16:53:20-08:00
New Revision: c9fce5f0c3a82cf037c288e840d857066aab75af

URL: https://github.com/llvm/llvm-project/commit/c9fce5f0c3a82cf037c288e840d857066aab75af
DIFF: https://github.com/llvm/llvm-project/commit/c9fce5f0c3a82cf037c288e840d857066aab75af.diff

LOG: X86: adjust the windows 64 calling convention for Swift

Adjust the Win64 calling convention for Swift to pass self in R13, which
is traditionally a CSR.  This makes the behaviour similar to the SysV CC
for Swift as well.  This should improve the argument passing on Windows,
although it comes at a high cost of ABI incompatibility.  Fortunately in
this case, there is no guarantee of ABI stability, and so we can make
this incompatible change.

Added: 
    llvm/test/CodeGen/X86/swiftself-win64.ll

Modified: 
    llvm/lib/Target/X86/X86CallingConv.td

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86CallingConv.td b/llvm/lib/Target/X86/X86CallingConv.td
index 3735fab818ce..45b814134c60 100644
--- a/llvm/lib/Target/X86/X86CallingConv.td
+++ b/llvm/lib/Target/X86/X86CallingConv.td
@@ -617,6 +617,9 @@ def CC_X86_Win64_C : CallingConv<[
   // A SwiftError is passed in R12.
   CCIfSwiftError<CCIfType<[i64], CCAssignToReg<[R12]>>>,
 
+  // Pass SwiftSelf in a callee saved register.
+  CCIfSwiftSelf<CCIfType<[i64], CCAssignToReg<[R13]>>>,
+
   // The 'CFGuardTarget' parameter, if any, is passed in RAX.
   CCIfCFGuardTarget<CCAssignToReg<[RAX]>>,
 

diff  --git a/llvm/test/CodeGen/X86/swiftself-win64.ll b/llvm/test/CodeGen/X86/swiftself-win64.ll
new file mode 100644
index 000000000000..0f3cf92cc4a1
--- /dev/null
+++ b/llvm/test/CodeGen/X86/swiftself-win64.ll
@@ -0,0 +1,63 @@
+; RUN: llc -verify-machineinstrs -mtriple=x86_64-unknown-windows-msvc -o - %s | FileCheck --check-prefix=CHECK --check-prefix=OPT %s
+; RUN: llc -O0 -verify-machineinstrs -mtriple=x86_64-unknown-windows-msvc -o - %s | FileCheck %s
+
+; Parameter with swiftself should be allocated to r13.
+; CHECK-LABEL: swiftself_param:
+; CHECK: movq %r13, %rax
+define i8 *@swiftself_param(i8* swiftself %addr0) {
+    ret i8 *%addr0
+}
+
+; Check that r13 is used to pass a swiftself argument.
+; CHECK-LABEL: call_swiftself:
+; CHECK: movq %rcx, %r13
+; CHECK: callq swiftself_param
+define i8 *@call_swiftself(i8* %arg) {
+  %res = call i8 *@swiftself_param(i8* swiftself %arg)
+  ret i8 *%res
+}
+
+; r13 should be saved by the callee even if used for swiftself
+; CHECK-LABEL: swiftself_clobber:
+; CHECK: pushq %r13
+; ...
+; CHECK: popq %r13
+define i8 *@swiftself_clobber(i8* swiftself %addr0) {
+  call void asm sideeffect "nop", "~{r13}"()
+  ret i8 *%addr0
+}
+
+; Demonstrate that we do not need any movs when calling multiple functions
+; with swiftself argument.
+; CHECK-LABEL: swiftself_passthrough:
+; OPT-NOT: mov{{.*}}r13
+; OPT: callq swiftself_param
+; OPT-NOT: mov{{.*}}r13
+; OPT-NEXT: callq swiftself_param
+define void @swiftself_passthrough(i8* swiftself %addr0) {
+  call i8 *@swiftself_param(i8* swiftself %addr0)
+  call i8 *@swiftself_param(i8* swiftself %addr0)
+  ret void
+}
+
+; We can use a tail call if the callee swiftself is the same as the caller one.
+; This should also work with fast-isel.
+; CHECK-LABEL: swiftself_tail:
+; CHECK: jmp swiftself_param
+; CHECK-NOT: ret
+define i8* @swiftself_tail(i8* swiftself %addr0) {
+  call void asm sideeffect "", "~{r13}"()
+  %res = tail call i8* @swiftself_param(i8* swiftself %addr0)
+  ret i8* %res
+}
+
+; We can not use a tail call if the callee swiftself is not the same as the
+; caller one.
+; CHECK-LABEL: swiftself_notail:
+; CHECK: movq %rcx, %r13
+; CHECK: callq swiftself_param
+; CHECK: retq
+define i8* @swiftself_notail(i8* swiftself %addr0, i8* %addr1) nounwind {
+  %res = tail call i8* @swiftself_param(i8* swiftself %addr1)
+  ret i8* %res
+}