Implement preserve_none for 32-bit x86

Author: brandtbucher

clang/include/clang/Basic/AttrDocs.td

@@ -6433,13 +6433,15 @@ experimental at this time.
 def PreserveNoneDocs : Documentation {
   let Category = DocCatCallingConvs;
   let Content = [{
-On X86-64 and AArch64 targets, this attribute changes the calling convention of a function.
+On X86, X86-64, and AArch64 targets, this attribute changes the calling convention of a function.
 The ``preserve_none`` calling convention tries to preserve as few general
 registers as possible. So all general registers are caller saved registers. It
 also uses more general registers to pass arguments. This attribute doesn't
 impact floating-point registers. ``preserve_none``'s ABI is still unstable, and
 may be changed in the future.
 
+- On X86, only ESP and EBP are preserved by the callee. Registers EDI, ESI, EDX,
+  ECX, and EAX now can be used to pass function arguments.
 - On X86-64, only RSP and RBP are preserved by the callee.
   Registers R12, R13, R14, R15, RDI, RSI, RDX, RCX, R8, R9, R11, and RAX now can
   be used to pass function arguments. Floating-point registers (XMMs/YMMs) still

clang/lib/Basic/Targets/X86.h

@@ -406,6 +406,7 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
     case CC_X86RegCall:
     case CC_C:
     case CC_PreserveMost:
+    case CC_PreserveNone:
     case CC_Swift:
     case CC_X86Pascal:
     case CC_IntelOclBicc:

clang/test/Sema/preserve-none-call-conv.c

@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 %s -fsyntax-only -triple x86_64-unknown-unknown -verify
 // RUN: %clang_cc1 %s -fsyntax-only -triple aarch64-unknown-unknown -verify
+// RUN: %clang_cc1 %s -fsyntax-only -triple i686-unknown-unknown -verify
 
 typedef void typedef_fun_t(int);
 

llvm/docs/LangRef.rst

@@ -463,7 +463,7 @@ added in the future:
     registers to pass arguments. This attribute doesn't impact non-general
     purpose registers (e.g. floating point registers, on X86 XMMs/YMMs).
     Non-general purpose registers still follow the standard C calling
-    convention. Currently it is for x86_64 and AArch64 only.
+    convention. Currently it is for x86, x86_64, and AArch64 only.
 "``cxx_fast_tlscc``" - The `CXX_FAST_TLS` calling convention for access functions
     Clang generates an access function to access C++-style Thread Local Storage
     (TLS). The access function generally has an entry block, an exit block and an

llvm/lib/Target/X86/X86CallingConv.td

@@ -1051,6 +1051,12 @@ def CC_X86_64_Preserve_None : CallingConv<[
   CCDelegateTo<CC_X86_64_C>
 ]>;
 
+def CC_X86_32_Preserve_None : CallingConv<[
+  // 32-bit variant of CC_X86_64_Preserve_None, above.
+  CCIfType<[i32], CCAssignToReg<[EDI, ESI, EDX, ECX, EAX]>>,
+  CCDelegateTo<CC_X86_32_C>
+]>;
+
 //===----------------------------------------------------------------------===//
 // X86 Root Argument Calling Conventions
 //===----------------------------------------------------------------------===//
@@ -1072,6 +1078,7 @@ def CC_X86_32 : CallingConv<[
   CCIfCC<"CallingConv::X86_RegCall",
     CCIfSubtarget<"isTargetWin32()", CCIfRegCallv4<CCDelegateTo<CC_X86_32_RegCallv4_Win>>>>,
   CCIfCC<"CallingConv::X86_RegCall", CCDelegateTo<CC_X86_32_RegCall>>,
+  CCIfCC<"CallingConv::PreserveNone", CCDelegateTo<CC_X86_32_Preserve_None>>,
 
   // Otherwise, drop to normal X86-32 CC
   CCDelegateTo<CC_X86_32_C>
@@ -1187,6 +1194,7 @@ def CSR_64_AllRegs_AVX512 : CalleeSavedRegs<(sub (add CSR_64_MostRegs, RAX,
                                                       (sequence "K%u", 0, 7)),
                                                  (sequence "XMM%u", 0, 15))>;
 def CSR_64_NoneRegs    : CalleeSavedRegs<(add RBP)>;
+def CSR_32_NoneRegs    : CalleeSavedRegs<(add EBP)>;
 
 // Standard C + YMM6-15
 def CSR_Win64_Intel_OCL_BI_AVX : CalleeSavedRegs<(add RBX, RBP, RDI, RSI, R12,

llvm/lib/Target/X86/X86RegisterInfo.cpp

@@ -316,7 +316,7 @@ X86RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
       return CSR_64_RT_AllRegs_AVX_SaveList;
     return CSR_64_RT_AllRegs_SaveList;
   case CallingConv::PreserveNone:
-    return CSR_64_NoneRegs_SaveList;
+    return Is64Bit ? CSR_64_NoneRegs_SaveList : CSR_32_NoneRegs_SaveList;
   case CallingConv::CXX_FAST_TLS:
     if (Is64Bit)
       return MF->getInfo<X86MachineFunctionInfo>()->isSplitCSR() ?
@@ -444,7 +444,7 @@ X86RegisterInfo::getCallPreservedMask(const MachineFunction &MF,
       return CSR_64_RT_AllRegs_AVX_RegMask;
     return CSR_64_RT_AllRegs_RegMask;
   case CallingConv::PreserveNone:
-    return CSR_64_NoneRegs_RegMask;
+    return Is64Bit ? CSR_64_NoneRegs_RegMask : CSR_32_NoneRegs_RegMask;
   case CallingConv::CXX_FAST_TLS:
     if (Is64Bit)
       return CSR_64_TLS_Darwin_RegMask;

llvm/test/CodeGen/X86/preserve_none_swift.ll

@@ -1,4 +1,5 @@
 ; RUN: not llc -mtriple=x86_64 %s -o - 2>&1 | FileCheck %s
+; RUN: not llc -mtriple=i686 %s -o - 2>&1 | FileCheck %s
 
 ; Swift attributes should not be used with preserve_none.