[llvm] r262465 - [X86] Permit reading of the FLAGS register without it being previously defined

[David Majnemer via llvm-commits]

Author: majnemer
Date: Wed Mar  2 00:46:52 2016
New Revision: 262465

URL: http://llvm.org/viewvc/llvm-project?rev=262465&view=rev
Log:
[X86] Permit reading of the FLAGS register without it being previously defined

We modeled the RDFLAGS{32,64} operations as "using" {E,R}FLAGS.
While technically correct, this is not be desirable for folks who want
to examine aspects of the FLAGS register which are not related to
computation like whether or not CPUID is a valid instruction.

Differential Revision: http://reviews.llvm.org/D17782

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
    llvm/trunk/lib/Target/X86/X86InstrInfo.td
    llvm/trunk/test/CodeGen/X86/x86-64-flags-intrinsics.ll
    llvm/trunk/test/CodeGen/X86/x86-flags-intrinsics.ll

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=262465&r1=262464&r2=262465&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Wed Mar  2 00:46:52 2016
@@ -23255,7 +23255,12 @@ X86TargetLowering::EmitInstrWithCustomIn
         MI->getOpcode() == X86::RDFLAGS32 ? X86::PUSHF32 : X86::PUSHF64;
     unsigned Pop =
         MI->getOpcode() == X86::RDFLAGS32 ? X86::POP32r : X86::POP64r;
-    BuildMI(*BB, MI, DL, TII->get(PushF));
+    MachineInstr *Push = BuildMI(*BB, MI, DL, TII->get(PushF));
+    // Permit reads of the FLAGS register without it being defined.
+    // This intrinsic exists to read external processor state in flags, such as
+    // the trap flag, interrupt flag, and direction flag, none of which are
+    // modeled by the backend.
+    Push->getOperand(2).setIsUndef();
     BuildMI(*BB, MI, DL, TII->get(Pop), MI->getOperand(0).getReg());
 
     MI->eraseFromParent(); // The pseudo is gone now.

Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.td
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.td?rev=262465&r1=262464&r2=262465&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86InstrInfo.td (original)
+++ llvm/trunk/lib/Target/X86/X86InstrInfo.td Wed Mar  2 00:46:52 2016
@@ -1122,12 +1122,12 @@ def PUSH32rmm: I<0xFF, MRM6m, (outs), (i
 
 let mayLoad = 1, mayStore = 1, usesCustomInserter = 1,
     SchedRW = [WriteRMW], Defs = [ESP] in {
-  let Uses = [ESP, EFLAGS] in
+  let Uses = [ESP] in
   def RDFLAGS32 : PseudoI<(outs GR32:$dst), (ins),
                    [(set GR32:$dst, (int_x86_flags_read_u32))]>,
                 Requires<[Not64BitMode]>;
 
-  let Uses = [RSP, EFLAGS] in
+  let Uses = [RSP] in
   def RDFLAGS64 : PseudoI<(outs GR64:$dst), (ins),
                    [(set GR64:$dst, (int_x86_flags_read_u64))]>,
                 Requires<[In64BitMode]>;

Modified: llvm/trunk/test/CodeGen/X86/x86-64-flags-intrinsics.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/x86-64-flags-intrinsics.ll?rev=262465&r1=262464&r2=262465&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/x86-64-flags-intrinsics.ll (original)
+++ llvm/trunk/test/CodeGen/X86/x86-64-flags-intrinsics.ll Wed Mar  2 00:46:52 2016
@@ -1,4 +1,4 @@
-; RUN: llc < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs < %s | FileCheck %s
 target triple = "x86_64-pc-win32"
 
 declare i64 @llvm.x86.flags.read.u64()

Modified: llvm/trunk/test/CodeGen/X86/x86-flags-intrinsics.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/x86-flags-intrinsics.ll?rev=262465&r1=262464&r2=262465&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/x86-flags-intrinsics.ll (original)
+++ llvm/trunk/test/CodeGen/X86/x86-flags-intrinsics.ll Wed Mar  2 00:46:52 2016
@@ -1,4 +1,4 @@
-; RUN: llc < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs < %s | FileCheck %s
 target triple = "i686-pc-win32"
 
 declare i32 @llvm.x86.flags.read.u32()