[PATCH] Don't force the use of a base pointer with MS inline asm

[Reid Kleckner]

    - Add a fatal error.

http://llvm-reviews.chandlerc.com/D1317

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D1317?vs=3269&id=3460#toc

Files:
  lib/Target/X86/X86RegisterInfo.cpp
  test/CodeGen/X86/inline-asm-stack-realign.ll
  test/CodeGen/X86/ms-inline-asm.ll

Index: lib/Target/X86/X86RegisterInfo.cpp
===================================================================
--- lib/Target/X86/X86RegisterInfo.cpp
+++ lib/Target/X86/X86RegisterInfo.cpp
@@ -340,6 +340,11 @@
         "Stack realignment in presence of dynamic allocas is not supported with"
         "this calling convention.");
 
+    if (MF.hasMSInlineAsm())
+      report_fatal_error(
+        "Stack realignment in the presence of stack-adjusting inline assembly "
+        "is not supported");
+
     for (MCSubRegIterator I(getBaseRegister(), this, /*IncludeSelf=*/true);
          I.isValid(); ++I)
       Reserved.set(*I);
@@ -396,18 +401,16 @@
    if (!EnableBasePointer)
      return false;
 
-   // When we need stack realignment and there are dynamic allocas, we can't
-   // reference off of the stack pointer, so we reserve a base pointer.
-   //
-   // This is also true if the function contain MS-style inline assembly.  We
-   // do this because if any stack changes occur in the inline assembly, e.g.,
-   // "pusha", then any C local variable or C argument references in the
-   // inline assembly will be wrong because the SP is not properly tracked.
-   if ((needsStackRealignment(MF) && MFI->hasVarSizedObjects()) ||
-       MF.hasMSInlineAsm())
-     return true;
-
-   return false;
+   // When we need stack realignment, we can't address the stack from the frame
+   // pointer.  When we have dynamic allocas or MS inline asm, we can't address
+   // variables from the stack pointer.  MS inline asm can reference locals
+   // while also adjusting the stack pointer.  When we can't use both the SP and
+   // the FP, we need a separate base pointer register.
+   // FIXME: gcc inline asm can also adjust the stack pointer if it lists esp as
+   // a clobber, but LLVM does not support that.
+   bool CantUseFP = needsStackRealignment(MF);
+   bool CantUseSP = MFI->hasVarSizedObjects() || MF.hasMSInlineAsm();
+   return CantUseFP && CantUseSP;
 }
 
 bool X86RegisterInfo::canRealignStack(const MachineFunction &MF) const {
Index: test/CodeGen/X86/inline-asm-stack-realign.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/inline-asm-stack-realign.ll
@@ -0,0 +1,16 @@
+; RUN: not llc -march x86 %s 2>&1 | FileCheck %s
+
+; Realigning the stack and referring to local stack vars through memory in
+; inline asm with this many clobbers is impossible.
+; FIXME: LLVM could do better here by looking at the list of clobbers.
+
+; CHECK: Stack realignment in presence of MS inline asm is not supported
+
+define i32 @foo() {
+entry:
+  %r = alloca i32, align 16
+  store i32 -1, i32* %r, align 16
+  call void asm sideeffect inteldialect "pusha\0A\09xor eax, eax\0A\09xor ebx, ebx\0A\09xor ecx, ecx\0A\09xor edx, edx\0A\09xor esi, esi\0A\09xor edi, edi\0A\09mov dword ptr $0, esi\0A\09popa", "=*m,~{eax},~{ebx},~{ecx},~{edi},~{edx},~{esi},~{dirflag},~{fpsr},~{flags}"(i32* %r) #1
+  %0 = load i32* %r, align 16
+  ret i32 %0
+}
Index: test/CodeGen/X86/ms-inline-asm.ll
===================================================================
--- test/CodeGen/X86/ms-inline-asm.ll
+++ test/CodeGen/X86/ms-inline-asm.ll
@@ -103,8 +103,8 @@
 ; CHECK: {{## InlineAsm End|#NO_APP}}
 ; CHECK: {{## InlineAsm Start|#APP}}
 ; CHECK: .intel_syntax
-; CHECK: mov dword ptr [esi], edi
+; CHECK: mov dword ptr [ebp - 8], edi
 ; CHECK: .att_syntax
 ; CHECK: {{## InlineAsm End|#NO_APP}}
-; CHECK: movl (%esi), %eax
+; CHECK: movl -8(%ebp), %eax
 }
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D1317.2.patch
Type: text/x-patch
Size: 3507 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130813/35e9b6bd/attachment.bin>