AArch64: correct preserve_most and preserve_all on Windows

[compnerd]

This fixes register information handling for the preserve_most and preserve_all calling conventions on Windows ARM64.

The root issue was cascading if statements whose behavior depended on their order. This patch makes the minimal, tactical change needed for Swift’s two calling conventions, unblocking current work. A broader refactor to remove the ordering dependency is still desired and will follow in a subsequent PR.

[llvmbot]

@llvm/pr-subscribers-platform-windows

@llvm/pr-subscribers-backend-aarch64

Author: Saleem Abdulrasool (compnerd)

Changes

This fixes register information handling for the preserve_most and preserve_all calling conventions on Windows ARM64.

The root issue was cascading if statements whose behavior depended on their order. This patch makes the minimal, tactical change needed for Swift’s two calling conventions, unblocking current work. A broader refactor to remove the ordering dependency is still desired and will follow in a subsequent PR.

---

Full diff: https://github.com/llvm/llvm-project/pull/166436.diff

3 Files Affected:

• (modified) llvm/lib/Target/AArch64/AArch64CallingConvention.td (+6)
• (modified) llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp (+10-4)
• (modified) llvm/test/CodeGen/AArch64/preserve_mostcc.ll (+24-14)

diff --git a/llvm/lib/Target/AArch64/AArch64CallingConvention.td b/llvm/lib/Target/AArch64/AArch64CallingConvention.td
index 1b5a713bffdc9..34c85d588f9c4 100644
--- a/llvm/lib/Target/AArch64/AArch64CallingConvention.td
+++ b/llvm/lib/Target/AArch64/AArch64CallingConvention.td
@@ -601,6 +601,12 @@ def CSR_Win_AArch64_AAPCS_SwiftError
 def CSR_Win_AArch64_AAPCS_SwiftTail
     : CalleeSavedRegs<(sub CSR_Win_AArch64_AAPCS, X20, X22)>;
 
+def CSR_Win_AArch64_RT_MostRegs
+    : CalleeSavedRegs<(add CSR_Win_AArch64_AAPCS, (sequence "X%u", 9, 15))>;
+
+def CSR_Win_AArch64_RT_AllRegs
+    : CalleeSavedRegs<(add CSR_Win_AArch64_RT_MostRegs, (sequence "Q%u", 8, 31))>;
+
 // The Control Flow Guard check call uses a custom calling convention that also
 // preserves X0-X8 and Q0-Q7.
 def CSR_Win_AArch64_CFGuard_Check : CalleeSavedRegs<(add CSR_Win_AArch64_AAPCS,
diff --git a/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp b/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp
index 5bfb19d9a7e61..061702ac11eb2 100644
--- a/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp
@@ -90,6 +90,16 @@ AArch64RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
   if (MF->getSubtarget<AArch64Subtarget>().isTargetDarwin())
     return getDarwinCalleeSavedRegs(MF);
 
+  if (MF->getFunction().getCallingConv() == CallingConv::PreserveMost)
+    return MF->getSubtarget<AArch64Subtarget>().isTargetWindows()
+        ? CSR_Win_AArch64_RT_MostRegs_SaveList
+        : CSR_AArch64_RT_MostRegs_SaveList;
+
+  if (MF->getFunction().getCallingConv() == CallingConv::PreserveAll)
+    return MF->getSubtarget<AArch64Subtarget>().isTargetWindows()
+        ? CSR_Win_AArch64_RT_AllRegs_SaveList
+        : CSR_AArch64_RT_AllRegs_SaveList;
+
   if (MF->getFunction().getCallingConv() == CallingConv::CFGuard_Check)
     return CSR_Win_AArch64_CFGuard_Check_SaveList;
   if (MF->getSubtarget<AArch64Subtarget>().isTargetWindows()) {
@@ -138,10 +148,6 @@ AArch64RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
     return CSR_AArch64_AAPCS_SwiftError_SaveList;
   if (MF->getFunction().getCallingConv() == CallingConv::SwiftTail)
     return CSR_AArch64_AAPCS_SwiftTail_SaveList;
-  if (MF->getFunction().getCallingConv() == CallingConv::PreserveMost)
-    return CSR_AArch64_RT_MostRegs_SaveList;
-  if (MF->getFunction().getCallingConv() == CallingConv::PreserveAll)
-    return CSR_AArch64_RT_AllRegs_SaveList;
   if (MF->getFunction().getCallingConv() == CallingConv::Win64)
     // This is for OSes other than Windows; Windows is a separate case further
     // above.
diff --git a/llvm/test/CodeGen/AArch64/preserve_mostcc.ll b/llvm/test/CodeGen/AArch64/preserve_mostcc.ll
index 7f0968c8eb339..75c8567e2095e 100644
--- a/llvm/test/CodeGen/AArch64/preserve_mostcc.ll
+++ b/llvm/test/CodeGen/AArch64/preserve_mostcc.ll
@@ -1,4 +1,5 @@
-; RUN: llc < %s -mtriple=arm64-apple-ios-8.0.0 | FileCheck %s
+; RUN: llc < %s -mtriple=arm64-apple-ios-8.0.0 | FileCheck -check-prefix CHECK -check-prefix CHECK-DARWIN %s
+; RUN: llc < %s -mtriple=aarch64-unknown-windiws-msvc | FileCheck -check-prefix CHECK -check-prefix CHECK-WIN %s
 
 declare void @standard_cc_func()
 declare preserve_mostcc void @preserve_mostcc_func()
@@ -8,18 +9,26 @@ declare preserve_mostcc void @preserve_mostcc_func()
 define preserve_mostcc void @preserve_mostcc1() nounwind {
 entry:
 ;CHECK-LABEL: preserve_mostcc1
-;CHECK-NOT:   stp
-;CHECK-NOT:   str
-;CHECK:       str     x15
-;CHECK-NEXT:  stp     x14, x13,
-;CHECK-NEXT:  stp     x12, x11,
-;CHECK-NEXT:  stp     x10, x9,
-;CHECK:       bl      _standard_cc_func
+;CHECK-DARWIN-NOT:   stp
+;CHECK-DARWIN-NOT:   str
+;CHECK-DARWIN:       str     x15
+;CHECK-DARWIN-NEXT:  stp     x14, x13,
+;CHECK-DARWIN-NEXT:  stp     x12, x11,
+;CHECK-DARWIN-NEXT:  stp     x10, x9,
+;CHECK-WIN:       stp     x15, x14
+;CHECK-WIN-NEXT:  stp     x13, x12,
+;CHECK-WIN-NEXT:  stp     x11, x10,
+;CHECK-WIN-NEXT:  stp     x9, x30
+;CHECK:       bl      {{_?}}standard_cc_func
   call void @standard_cc_func()
-;CHECK:       ldp     x10, x9,
-;CHECK-NEXT:  ldp     x12, x11,
-;CHECK-NEXT:  ldp     x14, x13,
-;CHECK-NEXT:  ldr     x15
+;CHECK-DARWIN:       ldp     x10, x9,
+;CHECK-DARWIN-NEXT:  ldp     x12, x11,
+;CHECK-DARWIN-NEXT:  ldp     x14, x13,
+;CHECK-DARWIN-NEXT:  ldr     x15
+;CHECK-WIN:       ldp     x9, x30
+;CHECK-WIN-NEXT:  ldp     x11, x10,
+;CHECK-WIN-NEXT:  ldp     x13, x12,
+;CHECK-WIN-NEXT:  ldp     x15, x14,
   ret void
 }
 
@@ -31,9 +40,10 @@ define preserve_mostcc void @preserve_mostcc2() nounwind {
 entry:
 ;CHECK-LABEL: preserve_mostcc2
 ;CHECK-NOT: x14
-;CHECK:     stp     x29, x30,
+;CHECK-DARWIN:     stp     x29, x30,
+;CHECK-WIN:     str     x30
 ;CHECK-NOT: x14
-;CHECK:     bl      _preserve_mostcc_func
+;CHECK:     bl      {{_?}}preserve_mostcc_func
   call preserve_mostcc void @preserve_mostcc_func()
   ret void
 }

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