[X86] Don't clobber EBX in stackprobes

On X86, the stackprobe emission code chooses the R11D register, which
is illegal on i686. This ends up wrapping around to EBX, which does
not get properly callee-saved within the stack probing prologue,
clobbering the register for the callers.

We fix this by explicitly using EAX as the stack probe register.

Author: staticfloat

llvm/lib/Target/X86/X86FrameLowering.cpp

@@ -652,7 +652,9 @@ void X86FrameLowering::emitStackProbeInlineGenericLoop(
   MF.insert(MBBIter, testMBB);
   MF.insert(MBBIter, tailMBB);
 
-  Register FinalStackProbed = Uses64BitFramePtr ? X86::R11 : X86::R11D;
+  Register FinalStackProbed = Uses64BitFramePtr ? X86::R11
+                              : Is64Bit         ? X86::R11D
+                                                : X86::EAX;
   BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::COPY), FinalStackProbed)
       .addReg(StackPtr)
       .setMIFlag(MachineInstr::FrameSetup);
@@ -1073,7 +1075,9 @@ void X86FrameLowering::BuildStackAlignAND(MachineBasicBlock &MBB,
       MF.insert(MBBIter, bodyMBB);
       MF.insert(MBBIter, footMBB);
       const unsigned MovMIOpc = Is64Bit ? X86::MOV64mi32 : X86::MOV32mi;
-      Register FinalStackProbed = Uses64BitFramePtr ? X86::R11 : X86::R11D;
+      Register FinalStackProbed = Uses64BitFramePtr ? X86::R11
+                                  : Is64Bit         ? X86::R11D
+                                                    : X86::EAX;
 
       // Setup entry block
       {

llvm/test/CodeGen/X86/stack-clash-large.ll

@@ -1,5 +1,6 @@
-; RUN: llc -mtriple=x86_64-linux-android < %s | FileCheck -check-prefix=CHECK-X86-64 %s 
-; RUN: llc -mtriple=i686-linux-android < %s | FileCheck -check-prefix=CHECK-X86-32 %s 
+; RUN: llc -mtriple=x86_64-linux-android < %s | FileCheck -check-prefix=CHECK-X64 %s 
+; RUN: llc -mtriple=i686-linux-android < %s | FileCheck -check-prefix=CHECK-X86 %s 
+; RUN: llc -mtriple=x86_64-linux-gnux32 < %s | FileCheck -check-prefix=CHECK-X32 %s 
 
 define i32 @foo() local_unnamed_addr #0 {
 
@@ -14,40 +15,60 @@ define i32 @foo() local_unnamed_addr #0 {
 
 attributes #0 =  {"probe-stack"="inline-asm"}
 
-; CHECK-X86-64-LABEL: foo:
-; CHECK-X86-64:        # %bb.0:
-; CHECK-X86-64-NEXT:	movq	%rsp, %r11
-; CHECK-X86-64-NEXT:	subq	$69632, %r11 # imm = 0x11000
-; CHECK-X86-64-NEXT:   .LBB0_1:
-; CHECK-X86-64-NEXT:	subq	$4096, %rsp # imm = 0x1000
-; CHECK-X86-64-NEXT:	movq	$0, (%rsp)
-; CHECK-X86-64-NEXT:	cmpq	%r11, %rsp
-; CHECK-X86-64-NEXT:	jne	.LBB0_1
-; CHECK-X86-64-NEXT:# %bb.2:
-; CHECK-X86-64-NEXT:	subq    $2248, %rsp
-; CHECK-X86-64-NEXT:	.cfi_def_cfa_offset 71888
-; CHECK-X86-64-NEXT:	movl	$1, 264(%rsp)
-; CHECK-X86-64-NEXT:	movl	$1, 28664(%rsp)
-; CHECK-X86-64-NEXT:	movl	-128(%rsp), %eax
-; CHECK-X86-64-NEXT:	addq	$71880, %rsp # imm = 0x118C8
-; CHECK-X86-64-NEXT:	.cfi_def_cfa_offset 8
-; CHECK-X86-64-NEXT:	retq
+; CHECK-X64-LABEL: foo:
+; CHECK-X64:        # %bb.0:
+; CHECK-X64-NEXT:	movq	%rsp, %r11
+; CHECK-X64-NEXT:	subq	$69632, %r11 # imm = 0x11000
+; CHECK-X64-NEXT:   .LBB0_1:
+; CHECK-X64-NEXT:	subq	$4096, %rsp # imm = 0x1000
+; CHECK-X64-NEXT:	movq	$0, (%rsp)
+; CHECK-X64-NEXT:	cmpq	%r11, %rsp
+; CHECK-X64-NEXT:	jne	.LBB0_1
+; CHECK-X64-NEXT:# %bb.2:
+; CHECK-X64-NEXT:	subq    $2248, %rsp
+; CHECK-X64-NEXT:	.cfi_def_cfa_offset 71888
+; CHECK-X64-NEXT:	movl	$1, 264(%rsp)
+; CHECK-X64-NEXT:	movl	$1, 28664(%rsp)
+; CHECK-X64-NEXT:	movl	-128(%rsp), %eax
+; CHECK-X64-NEXT:	addq	$71880, %rsp # imm = 0x118C8
+; CHECK-X64-NEXT:	.cfi_def_cfa_offset 8
+; CHECK-X64-NEXT:	retq
+
+; CHECK-X86-LABEL: foo:
+; CHECK-X86:      # %bb.0:
+; CHECK-X86-NEXT:    movl    %esp, %eax
+; CHECK-X86-NEXT:    subl    $69632, %eax # imm = 0x11000
+; CHECK-X86-NEXT:    .LBB0_1: # =>This Inner Loop Header: Depth=1
+; CHECK-X86-NEXT:    subl    $4096, %esp # imm = 0x1000
+; CHECK-X86-NEXT:    movl    $0, (%esp)
+; CHECK-X86-NEXT:    cmpl    %eax, %esp
+; CHECK-X86-NEXT:    jne  .LBB0_1
+; CHECK-X86-NEXT:# %bb.2:
+; CHECK-X86-NEXT:    subl    $2380, %esp
+; CHECK-X86-NEXT:    .cfi_def_cfa_offset 72016
+; CHECK-X86-NEXT:    movl    $1, 392(%esp)
+; CHECK-X86-NEXT:    movl    $1, 28792(%esp)
+; CHECK-X86-NEXT:    movl    (%esp), %eax
+; CHECK-X86-NEXT:    addl    $72012, %esp # imm = 0x1194C
+; CHECK-X86-NEXT:    .cfi_def_cfa_offset 4
+; CHECK-X86-NEXT:    retl
+
+; CHECK-X32-LABEL: foo:
+; CHECK-X32:      # %bb.0:
+; CHECK-X32-NEXT:    movl    %esp, %r11d
+; CHECK-X32-NEXT:    subl    $69632, %r11d # imm = 0x11000
+; CHECK-X32-NEXT:    .LBB0_1: # =>This Inner Loop Header: Depth=1
+; CHECK-X32-NEXT:    subl    $4096, %esp # imm = 0x1000
+; CHECK-X32-NEXT:    movq    $0, (%esp)
+; CHECK-X32-NEXT:    cmpl    %r11d, %esp
+; CHECK-X32-NEXT:    jne  .LBB0_1
+; CHECK-X32-NEXT:# %bb.2:
+; CHECK-X32-NEXT:    subl    $2248, %esp
+; CHECK-X32-NEXT:    .cfi_def_cfa_offset 71888
+; CHECK-X32-NEXT:    movl    $1, 264(%esp)
+; CHECK-X32-NEXT:    movl    $1, 28664(%esp)
+; CHECK-X32-NEXT:    movl    -128(%esp), %eax
+; CHECK-X32-NEXT:    addl    $71880, %esp # imm = 0x118C8
+; CHECK-X32-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-X32-NEXT:    retq
 
-; CHECK-X86-32-LABEL: foo:
-; CHECK-X86-32:      # %bb.0:
-; CHECK-X86-32-NEXT:    movl    %esp, %r11d
-; CHECK-X86-32-NEXT:    subl    $69632, %r11d # imm = 0x11000
-; CHECK-X86-32-NEXT:    .LBB0_1: # =>This Inner Loop Header: Depth=1
-; CHECK-X86-32-NEXT:    subl    $4096, %esp # imm = 0x1000
-; CHECK-X86-32-NEXT:    movl    $0, (%esp)
-; CHECK-X86-32-NEXT:    cmpl    %r11d, %esp
-; CHECK-X86-32-NEXT:    jne  .LBB0_1
-; CHECK-X86-32-NEXT:# %bb.2:
-; CHECK-X86-32-NEXT:    subl    $2380, %esp
-; CHECK-X86-32-NEXT:    .cfi_def_cfa_offset 72016
-; CHECK-X86-32-NEXT:    movl    $1, 392(%esp)
-; CHECK-X86-32-NEXT:    movl    $1, 28792(%esp)
-; CHECK-X86-32-NEXT:    movl    (%esp), %eax
-; CHECK-X86-32-NEXT:    addl    $72012, %esp # imm = 0x1194C
-; CHECK-X86-32-NEXT:    .cfi_def_cfa_offset 4
-; CHECK-X86-32-NEXT:    retl