Revert the backend fatal error from r196939

The combination of inline asm, stack realignment, and dynamic allocas
turns out to be too common to reject out of hand.

ASan inserts empy inline asm fragments and uses aligned allocas.
Compiling any trivial function containing a dynamic alloca with ASan is
enough to trigger the check.

XFAIL the test cases that would be miscompiled and add one that uses the
relevant functionality.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196986 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 35 insertions, 11 deletions

diff --git a/lib/Target/X86/X86RegisterInfo.cpp b/lib/Target/X86/X86RegisterInfo.cpp
index d3d05cd83a..e6cd59397c 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);
diff --git a/test/CodeGen/X86/inline-asm-stack-realign.ll b/test/CodeGen/X86/inline-asm-stack-realign.ll
index 476a628c8b..de98200a3a 100644
--- a/test/CodeGen/X86/inline-asm-stack-realign.ll
+++ b/test/CodeGen/X86/inline-asm-stack-realign.ll
@@ -1,8 +1,8 @@
 ; RUN: not llc -mtriple=i686-pc-win32 < %s 2>&1 | FileCheck %s
 
-; We don't currently support realigning the stack and adjusting the stack
-; pointer in inline asm.  This commonly happens in MS inline assembly using
-; push and pop.
+; FIXME: This is miscompiled due to our unconditional use of ESI as the base
+; pointer.
+; XFAIL:
 
 ; CHECK: Stack realignment in presence of dynamic stack adjustments is not supported with inline assembly
 
diff --git a/test/CodeGen/X86/inline-asm-stack-realign2.ll b/test/CodeGen/X86/inline-asm-stack-realign2.ll
index 2f042e84c5..4861c2040e 100644
--- a/test/CodeGen/X86/inline-asm-stack-realign2.ll
+++ b/test/CodeGen/X86/inline-asm-stack-realign2.ll
@@ -1,7 +1,8 @@
 ; RUN: not llc -mtriple=i686-pc-win32 < %s 2>&1 | FileCheck %s
 
-; We don't currently support realigning the stack and adjusting the stack
-; pointer in inline asm.  This can even happen in GNU asm.
+; FIXME: This is miscompiled due to our unconditional use of ESI as the base
+; pointer.
+; XFAIL:
 
 ; CHECK: Stack realignment in presence of dynamic stack adjustments is not supported with inline assembly
 
diff --git a/test/CodeGen/X86/inline-asm-stack-realign3.ll b/test/CodeGen/X86/inline-asm-stack-realign3.ll
new file mode 100644
index 0000000000..cdb77ca3ea
--- /dev/null
+++ b/test/CodeGen/X86/inline-asm-stack-realign3.ll
@@ -0,0 +1,29 @@
+; RUN: llc -march=x86 < %s | FileCheck %s
+
+declare void @bar(i32* %junk)
+
+define i32 @foo(i1 %cond) {
+entry:
+  %r = alloca i32, align 128
+  store i32 -1, i32* %r, align 128
+  br i1 %cond, label %doit, label %skip
+
+doit:
+  call void asm sideeffect "xor %ecx, %ecx\0A\09mov %ecx, $0", "=*m,~{ecx},~{flags}"(i32* %r)
+  %junk = alloca i32
+  call void @bar(i32* %junk)
+  br label %skip
+
+skip:
+  %0 = load i32* %r, align 128
+  ret i32 %0
+}
+
+; CHECK-LABEL: foo:
+; CHECK: pushl %ebp
+; CHECK: andl $-128, %esp
+; CHECK: xor %ecx, %ecx
+; CHECK-NEXT: mov %ecx, (%esi)
+; CHECK: movl (%esi), %eax
+; CHECK: popl %ebp
+; CHECK: ret