Revert "Fix miscompile of MS inline assembly with stack realignment"

This reverts commit r196876.  Its tests failed on the bots, so I'll
figure it out tomorrow.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196879 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 15 deletions

diff --git a/lib/Target/X86/X86RegisterInfo.cpp b/lib/Target/X86/X86RegisterInfo.cpp
index d3d05cd83a..dbda556b1b 100644
--- a/lib/Target/X86/X86RegisterInfo.cpp
+++ b/lib/Target/X86/X86RegisterInfo.cpp
@@ -347,12 +347,6 @@ BitVector X86RegisterInfo::getReservedRegs(const MachineFunction &MF) const {
         "Stack realignment in presence of dynamic allocas is not supported with"
         "this calling convention.");
 
-    // FIXME: Do a proper analysis of the inline asm to see if it actually
-    // conflicts with the base register we chose.
-    if (MF.hasInlineAsm())
-      report_fatal_error("Stack realignment in presence of dynamic stack "
-                         "adjustments is not supported with inline assembly.");
-
     for (MCSubRegIterator I(getBaseRegister(), this, /*IncludeSelf=*/true);
          I.isValid(); ++I)
       Reserved.set(*I);
@@ -409,15 +403,18 @@ bool X86RegisterInfo::hasBasePointer(const MachineFunction &MF) const {
    if (!EnableBasePointer)
      return false;
 
-   // When we need stack realignment, we can't address the stack from the frame
-   // pointer.  When we have dynamic allocas or stack-adjusting 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.
-   bool CantUseFP = needsStackRealignment(MF);
-   bool CantUseSP =
-       MFI->hasVarSizedObjects() || MFI->hasInlineAsmWithSPAdjust();
-   return CantUseFP && CantUseSP;
+   // 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;
 }
 
 bool X86RegisterInfo::canRealignStack(const MachineFunction &MF) const {