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

Fixes a regression caused by D82439, in which IT blocks were no longer being
generated when -Oz is present. This was due to the CPSR register being marked as
dead, while this case was not accounted for.

Differential Revision: https://reviews.llvm.org/D83667

llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp

@@ -587,6 +587,13 @@ bool ARMBaseInstrInfo::DefinesPredicate(
     const MachineOperand &MO = MI.getOperand(i);
     if ((MO.isRegMask() && MO.clobbersPhysReg(ARM::CPSR)) ||
         (MO.isReg() && MO.isDef() && MO.getReg() == ARM::CPSR)) {
+
+      // 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())
+        continue;
+
       Pred.push_back(MO);
       Found = true;
     }

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

@@ -37,26 +37,25 @@ define i32 @test_values(i32 %a, i32 %b) minsize optsize {
 ; 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:    beq .LBB0_3
 ; 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:    cmp r2, #30
-; CHECK-V7M-NEXT:    beq .LBB0_8
-; CHECK-V7M-NEXT:    cbnz r2, .LBB0_6
+; 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:    cbnz r2, .LBB0_4
+; CHECK-V7M-NEXT:  .LBB0_2:
 ; CHECK-V7M-NEXT:    add r0, r1
 ; CHECK-V7M-NEXT:    bx lr
-; CHECK-V7M-NEXT:  .LBB0_5:
+; CHECK-V7M-NEXT:  .LBB0_3:
 ; 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:  .LBB0_4:
 ; CHECK-V7M-NEXT:    bx lr
 ; CHECK-V7M-NEXT:    .p2align 2
 ; CHECK-V7M-NEXT:  .LCPI0_0: