[PowerPC] Fix CR Bit spill pseudo expansion

The current CRBIT spill pseudo-op expansion creates a KILL instruction
that kills the CRBIT and defines the enclosing CR field. However, this
paints a false picture to the register allocator that all bits in the CR
field are killed so copies of other bits out of the field become dead and
removable.
This changes the expansion to preserve the KILL flag on the CRBIT as an
implicit use and to treat the CR field as an undef input.

Thanks to Hal Finkel for the review and Uli Weigand for implementation input.

Differential revision: https://reviews.llvm.org/D55996

llvm-svn: 350153

diff --git a/llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp b/llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp
index 96923a9..3d067aa 100644 (file)
--- a/llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCRegisterInfo.cpp
@@ -673,12 +673,15 @@ void PPCRegisterInfo::lowerCRBitSpilling(MachineBasicBlock::iterator II,
   unsigned Reg = MF.getRegInfo().createVirtualRegister(LP64 ? G8RC : GPRC);
   unsigned SrcReg = MI.getOperand(0).getReg();
 
-  BuildMI(MBB, II, dl, TII.get(TargetOpcode::KILL),
-          getCRFromCRBit(SrcReg))
-          .addReg(SrcReg, getKillRegState(MI.getOperand(0).isKill()));
-
+  // We need to move the CR field that contains the CR bit we are spilling.
+  // The super register may not be explicitly defined (i.e. it can be defined
+  // by a CR-logical that only defines the subreg) so we state that the CR
+  // field is undef. Also, in order to preserve the kill flag on the CR bit,
+  // we add it as an implicit use.
   BuildMI(MBB, II, dl, TII.get(LP64 ? PPC::MFOCRF8 : PPC::MFOCRF), Reg)
-      .addReg(getCRFromCRBit(SrcReg));
+      .addReg(getCRFromCRBit(SrcReg), RegState::Undef)
+      .addReg(SrcReg,
+              RegState::Implicit | getKillRegState(MI.getOperand(0).isKill()));
 
   // If the saved register wasn't CR0LT, shift the bits left so that the bit to
   // store is the first one. Mask all but that bit.

diff --git a/llvm/test/CodeGen/PowerPC/NoCRFieldRedefWhenSpillingCRBIT.mir b/llvm/test/CodeGen/PowerPC/NoCRFieldRedefWhenSpillingCRBIT.mir
new file mode 100644 (file)
index 0000000..be28ac3
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/NoCRFieldRedefWhenSpillingCRBIT.mir
@@ -0,0 +1,121 @@
+# RUN: llc -mcpu=pwr8 -mtriple=powerpc64le-unknown-linux-gnu -start-after \
+# RUN:   virtregrewriter -ppc-asm-full-reg-names -verify-machineinstrs %s \
+# RUN:   -o - | FileCheck %s
+
+--- |
+  ; ModuleID = 'a.ll'
+  source_filename = "a.c"
+  target datalayout = "e-m:e-i64:64-n32:64"
+  target triple = "powerpc64le-unknown-linux-gnu"
+  
+  ; Function Attrs: nounwind
+  define void @test(i32 signext %a6, i32 signext %a7, i32 signext %a17) local_unnamed_addr #0 {
+  entry:
+    %cmp27 = icmp slt i32 %a6, %a7
+    %cmp29 = icmp sgt i32 %a6, %a17
+    %or.cond781 = or i1 %cmp27, %cmp29
+    tail call void asm sideeffect "# nothing", "~{cr0},~{cr1},~{cr2},~{cr3},~{cr4},~{cr5},~{cr6},~{cr7},~{memory}"() #1, !srcloc !1
+    br label %if.end326
+  
+  if.end326:                                        ; preds = %entry
+    br i1 %or.cond781, label %if.then330, label %if.end331
+  
+  if.then330:                                       ; preds = %if.end326
+    unreachable
+  
+  if.end331:                                        ; preds = %if.end326
+    ret void
+  }
+  
+  ; Function Attrs: nounwind
+  declare void @llvm.stackprotector(i8*, i8**) #1
+  
+  attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="ppc64le" "target-features"="+altivec,+bpermd,+crypto,+direct-move,+extdiv,+htm,+power8-vector,+vsx,-power9-vector,-qpx" "unsafe-fp-math"="false" "use-soft-float"="false" }
+  attributes #1 = { nounwind }
+  
+  !llvm.ident = !{!0}
+  
+  !0 = !{!"clang version 8.0.0 (trunk 349357)"}
+  !1 = !{i32 3373}
+
+...
+---
+name:            test
+alignment:       4
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+registers:       []
+liveins:         
+  - { reg: '$x3', virtual-reg: '' }
+  - { reg: '$x4', virtual-reg: '' }
+  - { reg: '$x5', virtual-reg: '' }
+frameInfo:       
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       0
+  offsetAdjustment: 0
+  maxAlignment:    4
+  adjustsStack:    false
+  hasCalls:        false
+  stackProtector:  ''
+  maxCallFrameSize: 4294967295
+  cvBytesOfCalleeSavedRegisters: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  localFrameSize:  0
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:      []
+stack:           
+  - { id: 0, name: '', type: spill-slot, offset: 0, size: 4, alignment: 4, 
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 1, name: '', type: spill-slot, offset: 0, size: 4, alignment: 4, 
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 2, name: '', type: spill-slot, offset: 0, size: 4, alignment: 4, 
+      stack-id: 0, callee-saved-register: '', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+constants:       []
+body:             |
+  bb.0.entry:
+    liveins: $x3, $x4, $x5
+  
+    renamable $cr0 = CMPW renamable $r3, renamable $r4, implicit $x4
+    renamable $cr1 = CMPW renamable $r3, renamable $r5, implicit $x5, implicit killed $x3
+    renamable $cr5lt = CRNOR renamable $cr0lt, renamable $cr1gt, implicit killed $cr0
+    renamable $cr5gt = COPY renamable $cr1gt, implicit $cr1
+    ; CHECK: crnor 4*cr5+lt, lt, 4*cr1+gt
+    ; CHECK: cror 4*cr5+gt, 4*cr1+gt, 4*cr1+gt
+    SPILL_CRBIT killed renamable $cr5lt, 0, %stack.0 :: (store 4 into %stack.0)
+    renamable $cr1 = CMPW renamable $r4, renamable $r5, implicit killed $x5, implicit killed $x4
+    SPILL_CRBIT killed renamable $cr5gt, 0, %stack.1 :: (store 4 into %stack.1)
+    SPILL_CRBIT killed renamable $cr1gt, 0, %stack.2 :: (store 4 into %stack.2)
+    INLINEASM &"# nothing", 25, 12, implicit-def dead early-clobber $cr0, 12, implicit-def dead early-clobber $cr1, 12, implicit-def dead early-clobber $cr2, 12, implicit-def dead early-clobber $cr3, 12, implicit-def dead early-clobber $cr4, 12, implicit-def dead early-clobber $cr5, 12, implicit-def dead early-clobber $cr6, 12, implicit-def dead early-clobber $cr7, !1
+    BLR8 implicit $lr8, implicit $rm
+  
+  bb.1.if.end326:
+    successors: %bb.2(0x00000001), %bb.3(0x7fffffff)
+  
+    renamable $cr5lt = RESTORE_CRBIT 0, %stack.0 :: (load 4 from %stack.0)
+    renamable $cr5gt = RESTORE_CRBIT 0, %stack.1 :: (load 4 from %stack.1)
+    renamable $cr5lt = CROR killed renamable $cr5lt, killed renamable $cr5gt
+    BCn killed renamable $cr5lt, %bb.3
+    B %bb.2
+  
+  bb.2.if.then330:
+    successors: 
+  
+  
+  bb.3.if.end331:
+    BLR8 implicit $lr8, implicit $rm
+
+...