[AArch64][GlobalISel] Use ZExtValue for zext(xor) when invert tb(n)z

Currently, we use SExtValue to decide whether to invert tbz or tbnz.
However, for the case zext (xor x, c), we should use ZExt rather
than SExt otherwise we will generate totally opposite branches.

Reviewed By: paquette

Differential Revision: https://reviews.llvm.org/D108755

Author: guopeilin

llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp

@@ -1314,6 +1314,7 @@ static AArch64CC::CondCode changeICMPPredToAArch64CC(CmpInst::Predicate P) {
 static Register getTestBitReg(Register Reg, uint64_t &Bit, bool &Invert,
                               MachineRegisterInfo &MRI) {
   assert(Reg.isValid() && "Expected valid register!");
+  bool HasZext = false;
   while (MachineInstr *MI = getDefIgnoringCopies(Reg, MRI)) {
     unsigned Opc = MI->getOpcode();
 
@@ -1327,6 +1328,9 @@ static Register getTestBitReg(Register Reg, uint64_t &Bit, bool &Invert,
     // on the truncated x is the same as the bit number on x.
     if (Opc == TargetOpcode::G_ANYEXT || Opc == TargetOpcode::G_ZEXT ||
         Opc == TargetOpcode::G_TRUNC) {
+      if (Opc == TargetOpcode::G_ZEXT)
+        HasZext = true;
+
       Register NextReg = MI->getOperand(1).getReg();
       // Did we find something worth folding?
       if (!NextReg.isValid() || !MRI.hasOneNonDBGUse(NextReg))
@@ -1355,8 +1359,12 @@ static Register getTestBitReg(Register Reg, uint64_t &Bit, bool &Invert,
         std::swap(ConstantReg, TestReg);
         VRegAndVal = getConstantVRegValWithLookThrough(ConstantReg, MRI);
       }
-      if (VRegAndVal)
-        C = VRegAndVal->Value.getSExtValue();
+      if (VRegAndVal) {
+        if (HasZext)
+          C = VRegAndVal->Value.getZExtValue();
+        else
+          C = VRegAndVal->Value.getSExtValue();
+      }
       break;
     }
     case TargetOpcode::G_ASHR:

llvm/test/CodeGen/AArch64/GlobalISel/opt-fold-xor-tbz-tbnz.mir

@@ -117,6 +117,38 @@ body:             |
     RET_ReallyLR
 ...
 ---
+name:            dont_flip_eq_zext
+alignment:       4
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  ; CHECK-LABEL: name: dont_flip_eq_zext
+  ; CHECK: bb.0:
+  ; CHECK:   successors: %bb.0(0x40000000), %bb.1(0x40000000)
+  ; CHECK:   [[COPY:%[0-9]+]]:gpr32 = COPY $wzr
+  ; CHECK:   [[SUBREG_TO_REG:%[0-9]+]]:gpr64all = SUBREG_TO_REG 0, [[COPY]], %subreg.sub_32
+  ; CHECK:   [[COPY1:%[0-9]+]]:gpr64 = COPY [[SUBREG_TO_REG]]
+  ; CHECK:   TBNZX [[COPY1]], 63, %bb.1
+  ; CHECK:   B %bb.0
+  ; CHECK: bb.1:
+  ; CHECK:   RET_ReallyLR
+  bb.0:
+    successors: %bb.0(0x40000000), %bb.1(0x40000000)
+
+    %1:gpr(s32) = G_CONSTANT i32 0
+    %3:gpr(s32) = G_CONSTANT i32 -1
+    %4:gpr(s32) = G_XOR %1, %3
+    %5:gpr(s64) = G_ZEXT %4(s32)
+    %15:gpr(s64) = G_CONSTANT i64 0
+    %13:gpr(s32) = G_ICMP intpred(slt), %5(s64), %15
+    %7:gpr(s1) = G_TRUNC %13(s32)
+    G_BRCOND %7(s1), %bb.1
+    G_BR %bb.0
+  bb.1:
+    RET_ReallyLR
+...
+---
 name:            dont_flip_ne
 alignment:       4
 legalized:       true