[ARM] Fix IT block generation after Thumb2SizeReduce with -Oz

[NickGuy]

Summary

Fixes a regression caused by D82439, in which IT blocks were no longer being generated when -Oz is present.

[NickGuy]

Rebased atop changes to https://reviews.llvm.org/D88494

[SjoerdMeijer]

llvm/test/CodeGen/Thumb2/ifcvt-dead-predicate.ll

3 ↗

(On Diff #299624)

I think a MIR test would be better here.

[NickGuy]

I think a MIR test would be better here.

Done

[SjoerdMeijer]

llvm/test/CodeGen/Thumb2/ifcvt-dead-predicate.mir

50

Not sure if I follow this codegen or what to expect, but every time I look at this patch I need to get up to speed again. But to help me, and to be a bit annoying, can you upload a diff with just the changes ? So, locally add this test first, and then create the diff against that.

[NickGuy]

I appreciate that the history and context for this has been a bit obscured. Most of it can be gathered on the patch D83667

can you upload a diff with just the changes ?

Done

[SjoerdMeijer]

Thanks, LGTM

llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp

 }
 
 bool ARMBaseInstrInfo::ClobbersPredicate(MachineInstr &MI,
                                          std::vector<MachineOperand> &Pred,
                                          bool SkipDead) const {
   bool Found = false;
   for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
     const MachineOperand &MO = MI.getOperand(i);
-    if ((MO.isRegMask() && MO.clobbersPhysReg(ARM::CPSR)) ||
-        (MO.isReg() && MO.isDef() && MO.getReg() == ARM::CPSR)) {
+    bool ClobbersCPSR = MO.isRegMask() && MO.clobbersPhysReg(ARM::CPSR);
+    bool IsCPSR = MO.isReg() && MO.isDef() && MO.getReg() == ARM::CPSR;
+    if (ClobbersCPSR || IsCPSR) {
+
+      // Filter out T1 instructions that have a dead CPSR,
+      // allowing IT blocks to be generated containing T1 instructions
+      const MCInstrDesc &MCID = MI.getDesc();
+      if (MCID.TSFlags & ARMII::ThumbArithFlagSetting && MO.isDead() &&
+          SkipDead)
+        continue;
+
       Pred.push_back(MO);
       Found = true;
     }
   }
 
   return Found;
 }
 

llvm/test/CodeGen/Thumb2/constant-hoisting.ll

 ; CHECK-V6M-NEXT:    .long 537923600
 ;
 ; CHECK-V7M-LABEL: test_values:
 ; CHECK-V7M:         mov r2, r0
 ; CHECK-V7M-NEXT:    ldr r0, .LCPI0_0
 ; CHECK-V7M-NEXT:    cmp r2, #50
 ; CHECK-V7M-NEXT:    beq .LBB0_5
 ; CHECK-V7M-NEXT:    cmp r2, #1
-; CHECK-V7M-NEXT:    beq .LBB0_7
+; CHECK-V7M-NEXT:    ittt eq
+; CHECK-V7M-NEXT:    addeq r0, r1
+; CHECK-V7M-NEXT:    addeq r0, #1
+; CHECK-V7M-NEXT:    bxeq lr
+; CHECK-V7M-NEXT:  .LBB0_2:
 ; CHECK-V7M-NEXT:    cmp r2, #30
-; CHECK-V7M-NEXT:    beq .LBB0_8
+; CHECK-V7M-NEXT:    ittt eq
+; CHECK-V7M-NEXT:    addeq r0, r1
+; CHECK-V7M-NEXT:    addeq r0, #2
+; CHECK-V7M-NEXT:    bxeq lr
+; CHECK-V7M-NEXT:  .LBB0_3:
 ; CHECK-V7M-NEXT:    cbnz r2, .LBB0_6
 ; CHECK-V7M-NEXT:    add r0, r1
 ; CHECK-V7M-NEXT:    bx lr
 ; CHECK-V7M-NEXT:  .LBB0_5:
 ; CHECK-V7M-NEXT:    add r0, r1
 ; CHECK-V7M-NEXT:    adds r0, #4
 ; CHECK-V7M-NEXT:  .LBB0_6:
 ; CHECK-V7M-NEXT:    bx lr
-; CHECK-V7M-NEXT:  .LBB0_7:
-; CHECK-V7M-NEXT:    add r0, r1
-; CHECK-V7M-NEXT:    adds r0, #1
-; CHECK-V7M-NEXT:    bx lr
-; CHECK-V7M-NEXT:  .LBB0_8:
-; CHECK-V7M-NEXT:    add r0, r1
-; CHECK-V7M-NEXT:    adds r0, #2
-; CHECK-V7M-NEXT:    bx lr
 ; CHECK-V7M-NEXT:    .p2align 2
 ; CHECK-V7M-NEXT:  .LCPI0_0:
 ; CHECK-V7M-NEXT:    .long 537923600
 entry:
   switch i32 %a, label %return [
     i32 0, label %sw.bb
     i32 1, label %sw.bb1
     i32 30, label %sw.bb3

llvm/test/CodeGen/Thumb2/ifcvt-dead-predicate.mir

+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -o - %s -run-pass=if-converter -simplify-mir | FileCheck %s
+
+--- |
+  ; ModuleID = 'ifcvt-dead-predicate.ll'
+  source_filename = "ifcvt-dead-predicate.ll"
+  target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+  target triple = "thumbv7-unknown-linux-android16"
+
+  ; Function Attrs: minsize nounwind optsize ssp uwtable
+  define hidden zeroext i1 @branch_entry(i32* %command_set, i8* %requested_filename, i8** %filename_to_use) local_unnamed_addr #0 {
+  entry:
+    %0 = load i32, i32* %command_set, align 4
+    %and.i.i = and i32 %0, 128
+    %tobool.i.i.not = icmp eq i32 %and.i.i, 0
+    br i1 %tobool.i.i.not, label %land.end, label %land.rhs
+
+  land.rhs:                                         ; preds = %entry
+    %call1 = tail call zeroext i1 @branch_target(i8* %requested_filename, i8** %filename_to_use)
+    ret i1 %call1
+
+  land.end:                                         ; preds = %entry
+    ret i1 false
+  }
+
+  ; Function Attrs: minsize optsize
+  declare zeroext i1 @branch_target(i8*, i8**) local_unnamed_addr #1
+
+  attributes #0 = { minsize nounwind optsize ssp uwtable }
+  attributes #1 = { minsize optsize }
+
+...
+---
+name:            branch_entry
+alignment:       2
+tracksRegLiveness: true
+liveins:
+  - { reg: '$r0' }
+  - { reg: '$r1' }
+  - { reg: '$r2' }
+frameInfo:
+  maxAlignment:    1
+  maxCallFrameSize: 0
+machineFunctionInfo: {}
+body:             |
+  ; CHECK-LABEL: name: branch_entry
+  ; CHECK: bb.0.entry:
+  ; CHECK:   successors: %bb.1
+  ; CHECK:   liveins: $r0, $r1, $r2
+  ; CHECK:   renamable $r0 = tLDRBi killed renamable $r0, 0, 14 /* CC::al */, $noreg :: (load 1 from %ir.command_set, align 4)
+  ; CHECK:   dead renamable $r0, $cpsr = tLSLri killed renamable $r0, 24, 14 /* CC::al */, $noreg
+  ; CHECK:   $r0, dead $noreg = tMOVi8 0, 5 /* CC::pl */, $cpsr
+  ; CHECK:   tBX_RET 5 /* CC::pl */, killed $cpsr, implicit killed $r0
+  ; CHECK: bb.1.land.rhs:
+  ; CHECK:   liveins: $r1, $r2
+  ; CHECK:   $r0 = tMOVr killed $r1, 14 /* CC::al */, $noreg
+  ; CHECK:   $r1 = tMOVr killed $r2, 14 /* CC::al */, $noreg
+  ; CHECK:   tTAILJMPdND @branch_target, 14 /* CC::al */, $noreg, implicit $sp, implicit $sp, implicit $r0, implicit $r1
+  bb.0.entry:
+    successors: %bb.1, %bb.2
+    liveins: $r0, $r1, $r2
+
+    renamable $r0 = tLDRBi killed renamable $r0, 0, 14 /* CC::al */, $noreg :: (load 1 from %ir.command_set, align 4)
+    dead renamable $r0, $cpsr = tLSLri killed renamable $r0, 24, 14 /* CC::al */, $noreg
+    t2Bcc %bb.2, 4 /* CC::mi */, killed $cpsr
+
+  bb.1.land.end:
+    $r0, dead $cpsr = tMOVi8 0, 14 /* CC::al */, $noreg
+    tBX_RET 14 /* CC::al */, $noreg, implicit $r0
+
+  bb.2.land.rhs:
+    liveins: $r1, $r2
+
+    $r0 = tMOVr killed $r1, 14 /* CC::al */, $noreg
+    $r1 = tMOVr killed $r2, 14 /* CC::al */, $noreg
+    tTAILJMPdND @branch_target, 14 /* CC::al */, $noreg, implicit $sp, implicit $sp, implicit $r0, implicit $r1
+
+...