[llvm] r267634 - [X86] Make sure it is safe to clobber EFLAGS, if need be, when choosing

Fri Apr 29 16:21:46 PDT 2016

Merged in r268132.

Cheers,
Hans

On Fri, Apr 29, 2016 at 10:41 AM, Tom Stellard <tom at stellard.net> wrote:
> This looks good to me.  Hans can you merge it?  If not, I will do it.
>
> -Tom
>
> On Fri, Apr 29, 2016 at 09:53:01AM -0700, Nadav Rotem wrote:
>> LGTM.
>>
>> > On Apr 29, 2016, at 9:42 AM, Hans Wennborg <hans at chromium.org> wrote:
>> >
>> > +Tom: this might be a good candidate for 3.8.1.
>> > +Nadav for X86 ownership
>> >
>> > On Tue, Apr 26, 2016 at 4:44 PM, Quentin Colombet via llvm-commits
>> > <llvm-commits at lists.llvm.org> wrote:
>> >> Author: qcolombet
>> >> Date: Tue Apr 26 18:44:14 2016
>> >> New Revision: 267634
>> >>
>> >> URL: http://llvm.org/viewvc/llvm-project?rev=267634&view=rev
>> >> Log:
>> >> [X86] Make sure it is safe to clobber EFLAGS, if need be, when choosing
>> >> the prologue.
>> >>
>> >> Do not use basic blocks that have EFLAGS live-in as prologue if we need
>> >> to realign the stack. Realigning the stack uses AND instruction and this
>> >> clobbers EFLAGS.
>> >>
>> >> An other alternative would have been to save and restore EFLAGS around
>> >> the stack realignment code, but this is likely inefficient.
>> >>
>> >> Fixes PR27531.
>> >>
>> >> Added:
>> >>    llvm/trunk/test/CodeGen/X86/i686-win-shrink-wrapping.ll
>> >> Modified:
>> >>    llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
>> >>    llvm/trunk/lib/Target/X86/X86FrameLowering.h
>> >>
>> >> Modified: llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
>> >> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86FrameLowering.cpp?rev=267634&r1=267633&r2=267634&view=diff
>> >> ==============================================================================
>> >> --- llvm/trunk/lib/Target/X86/X86FrameLowering.cpp (original)
>> >> +++ llvm/trunk/lib/Target/X86/X86FrameLowering.cpp Tue Apr 26 18:44:14 2016
>> >> @@ -2609,6 +2609,12 @@ eliminateCallFramePseudoInstr(MachineFun
>> >>   return I;
>> >> }
>> >>
>> >> +bool X86FrameLowering::canUseAsPrologue(const MachineBasicBlock &MBB) const {
>> >> +  assert(MBB.getParent() && "Block is not attached to a function!");
>> >> +  const MachineFunction &MF = *MBB.getParent();
>> >> +  return !TRI->needsStackRealignment(MF) || !MBB.isLiveIn(X86::EFLAGS);
>> >> +}
>> >> +
>> >> bool X86FrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const {
>> >>   assert(MBB.getParent() && "Block is not attached to a function!");
>> >>
>> >>
>> >> Modified: llvm/trunk/lib/Target/X86/X86FrameLowering.h
>> >> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86FrameLowering.h?rev=267634&r1=267633&r2=267634&view=diff
>> >> ==============================================================================
>> >> --- llvm/trunk/lib/Target/X86/X86FrameLowering.h (original)
>> >> +++ llvm/trunk/lib/Target/X86/X86FrameLowering.h Tue Apr 26 18:44:14 2016
>> >> @@ -127,6 +127,16 @@ public:
>> >>   /// Check that LEA can be used on SP in an epilogue sequence for \p MF.
>> >>   bool canUseLEAForSPInEpilogue(const MachineFunction &MF) const;
>> >>
>> >> +  /// Check whether or not the given \p MBB can be used as a prologue
>> >> +  /// for the target.
>> >> +  /// The prologue will be inserted first in this basic block.
>> >> +  /// This method is used by the shrink-wrapping pass to decide if
>> >> +  /// \p MBB will be correctly handled by the target.
>> >> +  /// As soon as the target enable shrink-wrapping without overriding
>> >> +  /// this method, we assume that each basic block is a valid
>> >> +  /// prologue.
>> >> +  bool canUseAsPrologue(const MachineBasicBlock &MBB) const override;
>> >> +
>> >>   /// Check whether or not the given \p MBB can be used as a epilogue
>> >>   /// for the target.
>> >>   /// The epilogue will be inserted before the first terminator of that block.
>> >>
>> >> Added: llvm/trunk/test/CodeGen/X86/i686-win-shrink-wrapping.ll
>> >> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/i686-win-shrink-wrapping.ll?rev=267634&view=auto
>> >> ==============================================================================
>> >> --- llvm/trunk/test/CodeGen/X86/i686-win-shrink-wrapping.ll (added)
>> >> +++ llvm/trunk/test/CodeGen/X86/i686-win-shrink-wrapping.ll Tue Apr 26 18:44:14 2016
>> >> @@ -0,0 +1,44 @@
>> >> +; RUN: llc %s -o - -enable-shrink-wrap=true | FileCheck %s --check-prefix=CHECK --check-prefix=ENABLE
>> >> +; RUN: llc %s -o - -enable-shrink-wrap=false | FileCheck %s --check-prefix=CHECK --check-prefix=DISABLE
>> >> +target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
>> >> +target triple = "i686-pc-windows-msvc18.0.0"
>> >> +
>> >> +%struct.S = type { i32 }
>> >> +
>> >> +; Check that we do not use a basic block that has EFLAGS as live-in
>> >> +; if we need to realign the stack.
>> >> +; PR27531.
>> >> +; CHECK-LABEL: stackRealignment:
>> >> +; Prologue code.
>> >> +; CHECK: pushl
>> >> +; Make sure we actually perform some stack realignment.
>> >> +; CHECK: andl ${{[-0-9]+}}, %esp
>> >> +; This is the end of the entry block.
>> >> +; The prologue should have happened before that point because past
>> >> +; this point, EFLAGS is live.
>> >> +; CHECK: jg
>> >> +define x86_thiscallcc void @stackRealignment(%struct.S* %this) {
>> >> +entry:
>> >> +  %data = alloca [1 x i32], align 4
>> >> +  %d = alloca double, align 8
>> >> +  %tmp = bitcast [1 x i32]* %data to i8*
>> >> +  %arrayinit.begin = getelementptr inbounds [1 x i32], [1 x i32]* %data, i32 0, i32 0
>> >> +  %x_ = getelementptr inbounds %struct.S, %struct.S* %this, i32 0, i32 0
>> >> +  %tmp1 = load i32, i32* %x_, align 4
>> >> +  %cmp = icmp sgt i32 %tmp1, 32
>> >> +  %cond = select i1 %cmp, i32 42, i32 128
>> >> +  store i32 %cond, i32* %arrayinit.begin, align 4
>> >> +  %cmp3 = icmp slt i32 %tmp1, 32
>> >> +  br i1 %cmp3, label %cleanup, label %if.end
>> >> +
>> >> +if.end:                                           ; preds = %entry
>> >> +  %tmp2 = bitcast double* %d to i8*
>> >> +  call x86_thiscallcc void @bar(%struct.S* nonnull %this, i32* %arrayinit.begin, double* nonnull %d)
>> >> +  br label %cleanup
>> >> +
>> >> +cleanup:                                          ; preds = %if.end, %entry
>> >> +  ret void
>> >> +}
>> >> +
>> >> +; Function Attrs: optsize
>> >> +declare x86_thiscallcc void @bar(%struct.S*, i32*, double*)
>>