[Arm64EC] Improve alignment mangling in arm64ec thunks.

[efriedma-quic]

In some cases, MSVC's mangling for arm64ec thunks includes the alignment of a struct. I added some code to try to match... but it never really worked right. The issues:

• Alignment is only mangled if it's 16 or more (I guess the default is supposed to be 8).
• Alignment isn't mangled on return values (since the memory is allocated by the caller).

The current patch leaves hooks to make alignment mangling work... but doesn't actually ever mangle alignment: clang never actually encodes a relevant alignment into the IR. Once we get clang to emit the real size/alignment of structs, we can start emitting it.

[llvmbot]

@llvm/pr-subscribers-backend-aarch64

Author: Eli Friedman (efriedma-quic)

Changes

In some cases, MSVC's mangling for arm64ec thunks includes the alignment of a struct. I added some code to try to match... but it never really worked right. The issues:

• Alignment is only mangled if it's 16 or more (I guess the default is supposed to be 8).
• Alignment isn't mangled on return values (since the memory is allocated by the caller).

The current patch leaves hooks to make alignment mangling work... but doesn't actually ever mangle alignment: clang never actually encodes a relevant alignment into the IR. Once we get clang to emit the real size/alignment of structs, we can start emitting it.

---

Full diff: https://github.com/llvm/llvm-project/pull/90115.diff

3 Files Affected:

• (modified) llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp (+4-3)
• (modified) llvm/test/CodeGen/AArch64/arm64ec-entry-thunks.ll (+3-3)
• (modified) llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll (+5-5)

diff --git a/llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp b/llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp
index 3bf6283b79e9b8..dddc181b031444 100644
--- a/llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp
@@ -178,13 +178,14 @@ void AArch64Arm64ECCallLowering::getThunkArgTypes(
   }
 
   for (unsigned E = FT->getNumParams(); I != E; ++I) {
-    Align ParamAlign = AttrList.getParamAlignment(I).valueOrOne();
 #if 0
     // FIXME: Need more information about argument size; see
     // https://reviews.llvm.org/D132926
     uint64_t ArgSizeBytes = AttrList.getParamArm64ECArgSizeBytes(I);
+    Align ParamAlign = AttrList.getParamAlignment(I).valueOrOne();
 #else
     uint64_t ArgSizeBytes = 0;
+    Align ParamAlign = Align();
 #endif
     Type *Arm64Ty, *X64Ty;
     canonicalizeThunkType(FT->getParamType(I), ParamAlign,
@@ -294,7 +295,7 @@ void AArch64Arm64ECCallLowering::canonicalizeThunkType(
     uint64_t TotalSizeBytes = ElementCnt * ElementSizePerBytes;
     if (ElementTy->isFloatTy() || ElementTy->isDoubleTy()) {
       Out << (ElementTy->isFloatTy() ? "F" : "D") << TotalSizeBytes;
-      if (Alignment.value() >= 8 && !T->isPointerTy())
+      if (Alignment.value() >= 16 && !Ret)
         Out << "a" << Alignment.value();
       Arm64Ty = T;
       if (TotalSizeBytes <= 8) {
@@ -325,7 +326,7 @@ void AArch64Arm64ECCallLowering::canonicalizeThunkType(
   Out << "m";
   if (TypeSize != 4)
     Out << TypeSize;
-  if (Alignment.value() >= 8 && !T->isPointerTy())
+  if (Alignment.value() >= 16 && !Ret)
     Out << "a" << Alignment.value();
   // FIXME: Try to canonicalize Arm64Ty more thoroughly?
   Arm64Ty = T;
diff --git a/llvm/test/CodeGen/AArch64/arm64ec-entry-thunks.ll b/llvm/test/CodeGen/AArch64/arm64ec-entry-thunks.ll
index bb9ba05f7a2724..c00c9bfe127e8a 100644
--- a/llvm/test/CodeGen/AArch64/arm64ec-entry-thunks.ll
+++ b/llvm/test/CodeGen/AArch64/arm64ec-entry-thunks.ll
@@ -223,8 +223,8 @@ define i8 @matches_has_sret() nounwind {
 
 %TSRet = type { i64, i64 }
 define void @has_aligned_sret(ptr align 32 sret(%TSRet)) nounwind {
-; CHECK-LABEL:    .def    $ientry_thunk$cdecl$m16a32$v;
-; CHECK:          .section        .wowthk$aa,"xr",discard,$ientry_thunk$cdecl$m16a32$v
+; CHECK-LABEL:    .def    $ientry_thunk$cdecl$m16$v;
+; CHECK:          .section        .wowthk$aa,"xr",discard,$ientry_thunk$cdecl$m16$v
 ; CHECK:          // %bb.0:
 ; CHECK-NEXT:     stp     q6, q7, [sp, #-176]!            // 32-byte Folded Spill
 ; CHECK-NEXT:     .seh_save_any_reg_px    q6, 176
@@ -457,7 +457,7 @@ define %T2 @simple_struct(%T1 %0, %T2 %1, %T3, %T4) nounwind {
 ; CHECK-NEXT:     .symidx $ientry_thunk$cdecl$i8$v
 ; CHECK-NEXT:     .word   1
 ; CHECK-NEXT:     .symidx "#has_aligned_sret"
-; CHECK-NEXT:     .symidx $ientry_thunk$cdecl$m16a32$v
+; CHECK-NEXT:     .symidx $ientry_thunk$cdecl$m16$v
 ; CHECK-NEXT:     .word   1
 ; CHECK-NEXT:     .symidx "#small_array"
 ; CHECK-NEXT:     .symidx $ientry_thunk$cdecl$m2$m2F8
diff --git a/llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll b/llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll
index 3b911e78aff2a4..7a40fcd85ac585 100644
--- a/llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll
+++ b/llvm/test/CodeGen/AArch64/arm64ec-exit-thunks.ll
@@ -236,8 +236,8 @@ declare void @has_sret(ptr sret([100 x i8])) nounwind;
 
 %TSRet = type { i64, i64 }
 declare void @has_aligned_sret(ptr align 32 sret(%TSRet)) nounwind;
-; CHECK-LABEL:    .def    $iexit_thunk$cdecl$m16a32$v;
-; CHECK:          .section        .wowthk$aa,"xr",discard,$iexit_thunk$cdecl$m16a32$v
+; CHECK-LABEL:    .def    $iexit_thunk$cdecl$m16$v;
+; CHECK:          .section        .wowthk$aa,"xr",discard,$iexit_thunk$cdecl$m16$v
 ; CHECK:          // %bb.0:
 ; CHECK-NEXT:     sub     sp, sp, #48
 ; CHECK-NEXT:     .seh_stackalloc 48
@@ -271,8 +271,8 @@ declare void @has_aligned_sret(ptr align 32 sret(%TSRet)) nounwind;
 ; CHECK:          adrp    x11, has_aligned_sret
 ; CHECK:          add     x11, x11, :lo12:has_aligned_sret
 ; CHECK:          ldr     x9, [x9, :lo12:__os_arm64x_check_icall]
-; CHECK:          adrp    x10, ($iexit_thunk$cdecl$m16a32$v)
-; CHECK:          add     x10, x10, :lo12:($iexit_thunk$cdecl$m16a32$v)
+; CHECK:          adrp    x10, ($iexit_thunk$cdecl$m16$v)
+; CHECK:          add     x10, x10, :lo12:($iexit_thunk$cdecl$m16$v)
 ; CHECK:          blr     x9
 ; CHECK:          .seh_startepilogue
 ; CHECK:          ldr     x30, [sp], #16                  // 8-byte Folded Reload
@@ -492,7 +492,7 @@ declare %T2 @simple_struct(%T1, %T2, %T3, %T4) nounwind;
 ; CHECK-NEXT:     .symidx has_sret
 ; CHECK-NEXT:     .word   0
 ; CHECK-NEXT:     .symidx has_aligned_sret
-; CHECK-NEXT:     .symidx $iexit_thunk$cdecl$m16a32$v
+; CHECK-NEXT:     .symidx $iexit_thunk$cdecl$m16$v
 ; CHECK-NEXT:     .word   4
 ; CHECK-NEXT:     .symidx "#has_aligned_sret$exit_thunk"
 ; CHECK-NEXT:     .symidx has_aligned_sret