[llvm] r214550 - MS inline asm: Use memory constraints for functions instead of registers

[Reid Kleckner]

Author: rnk
Date: Fri Aug  1 15:21:24 2014
New Revision: 214550

URL: http://llvm.org/viewvc/llvm-project?rev=214550&view=rev
Log:
MS inline asm: Use memory constraints for functions instead of registers

This is consistent with how we parse them in a standalone .s file, and
inline assembly shouldn't differ.

This fixes errors about requiring more registers than available in
cases like this:
  void f();
  void __declspec(naked) g() {
    __asm pusha
    __asm call f
    __asm popa
    __asm ret
  }

There are no registers available to pass the address of 'f' into the asm
blob.  The asm should now directly call 'f'.

Tests will land in Clang shortly.

Modified:
    llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp
    llvm/trunk/test/CodeGen/X86/ms-inline-asm.ll

Modified: llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp?rev=214550&r1=214549&r2=214550&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp (original)
+++ llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp Fri Aug  1 15:21:24 2014
@@ -731,6 +731,13 @@ private:
                     (X86::Mode64Bit | X86::Mode32Bit | X86::Mode16Bit)));
   }
 
+  unsigned getPointerWidth() {
+    if (is16BitMode()) return 16;
+    if (is32BitMode()) return 32;
+    if (is64BitMode()) return 64;
+    llvm_unreachable("invalid mode");
+  }
+
   bool isParsingIntelSyntax() {
     return getParser().getAssemblerDialect();
   }
@@ -982,15 +989,20 @@ std::unique_ptr<X86Operand> X86AsmParser
     unsigned SegReg, const MCExpr *Disp, unsigned BaseReg, unsigned IndexReg,
     unsigned Scale, SMLoc Start, SMLoc End, unsigned Size, StringRef Identifier,
     InlineAsmIdentifierInfo &Info) {
-  // If this is not a VarDecl then assume it is a FuncDecl or some other label
-  // reference.  We need an 'r' constraint here, so we need to create register
-  // operand to ensure proper matching.  Just pick a GPR based on the size of
-  // a pointer.
-  if (isa<MCSymbolRefExpr>(Disp) && !Info.IsVarDecl) {
-    unsigned RegNo =
-        is64BitMode() ? X86::RBX : (is32BitMode() ? X86::EBX : X86::BX);
-    return X86Operand::CreateReg(RegNo, Start, End, /*AddressOf=*/true,
-                                 SMLoc(), Identifier, Info.OpDecl);
+  // If we found a decl other than a VarDecl, then assume it is a FuncDecl or
+  // some other label reference.
+  if (isa<MCSymbolRefExpr>(Disp) && Info.OpDecl && !Info.IsVarDecl) {
+    // Insert an explicit size if the user didn't have one.
+    if (!Size) {
+      Size = getPointerWidth();
+      InstInfo->AsmRewrites->push_back(AsmRewrite(AOK_SizeDirective, Start,
+                                                  /*Len=*/0, Size));
+    }
+
+    // Create an absolute memory reference in order to match against
+    // instructions taking a PC relative operand.
+    return X86Operand::CreateMem(Disp, Start, End, Size, Identifier,
+                                 Info.OpDecl);
   }
 
   // We either have a direct symbol reference, or an offset from a symbol.  The

Modified: llvm/trunk/test/CodeGen/X86/ms-inline-asm.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/ms-inline-asm.ll?rev=214550&r1=214549&r2=214550&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/ms-inline-asm.ll (original)
+++ llvm/trunk/test/CodeGen/X86/ms-inline-asm.ll Fri Aug  1 15:21:24 2014
@@ -110,7 +110,7 @@ define i32 @t31() {
 entry:
   %val = alloca i32, align 64
   store i32 -1, i32* %val, align 64
-  call void asm sideeffect inteldialect "mov dword ptr $0, esp", "=*m,~{dirflag},~{fpsr},~{flags}"(i32* %val) #1
+  call void asm sideeffect inteldialect "mov dword ptr $0, esp", "=*m,~{dirflag},~{fpsr},~{flags}"(i32* %val)
   %sp = load i32* %val, align 64
   ret i32 %sp
 ; CHECK-LABEL: t31:
@@ -125,3 +125,12 @@ entry:
 ; CHECK: movl (%esp), %eax
 ; CHECK: ret
 }
+
+declare void @other_func()
+
+define void @naked() #0 {
+  call void asm sideeffect inteldialect "call dword ptr $0", "*m,~{eax},~{ebx},~{ecx},~{edx},~{edi},~{esi},~{esp},~{ebp},~{dirflag},~{fpsr},~{flags}"(void()* @other_func)
+  unreachable
+}
+
+attributes #0 = { naked }