[AArch64] Fix signed integer overflow in CSINC case

[vitalybuka]

Summary

https://lab.llvm.org/staging/#/builders/224/builds/2/steps/16/logs/stdio

[dmgreen]

SGTM

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

if (CTVal && CFVal && CTVal->isAllOnes() && CFVal->isZero()) {
 
         if ((TrueVal32 == FalseVal32 + 1) || (TrueVal32 + 1 == FalseVal32)) {
           Opcode = AArch64ISD::CSINC;
 
           if (TrueVal32 > FalseVal32) {
             Swap = true;
           }
         }
-        // 64-bit check whether we can use CSINC.
-      } else if ((TrueVal == FalseVal + 1) || (TrueVal + 1 == FalseVal)) {
+        // 64-bit check whether we can use CSINC. To avoid signed integer
+        // overflow the condition ignores wrap around, which is already
+        // handled by CSINV above.
+      } else if (1 ==
+                 std::max(TrueVal, FalseVal) - std::min(TrueVal, FalseVal)) {
         Opcode = AArch64ISD::CSINC;
 
         if (TrueVal > FalseVal) {
           Swap = true;
         }
       }
 
       // Swap TVal and FVal if necessary.

llvm/test/CodeGen/AArch64/arm64-csel.ll

 ; CHECK-NEXT:    cinc x0, x8, le
 ; CHECK-NEXT:    ret
 entry:
   %cmp = icmp sgt i64 %a, %b
   %. = select i1 %cmp, i64 1, i64 2
   ret i64 %.
 }
 
+; Regression test for TrueVal + 1 overflow
+define i64 @foo18_overflow1(i64 %a, i64 %b) nounwind readnone optsize ssp {
+; CHECK-LABEL: foo18_overflow1:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    cmp x0, x1
+; CHECK-NEXT:    mov x8, #9223372036854775807
+; CHECK-NEXT:    csel x0, x8, xzr, gt
+; CHECK-NEXT:    ret
+entry:
+  %cmp = icmp sgt i64 %a, %b
+  %. = select i1 %cmp, i64 9223372036854775807, i64 0
+  ret i64 %.
+}
+
+; Regression test for FalseVal + 1 overflow
+define i64 @foo18_overflow2(i64 %a, i64 %b) nounwind readnone optsize ssp {
+; CHECK-LABEL: foo18_overflow2:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    cmp x0, x1
+; CHECK-NEXT:    mov x8, #9223372036854775807
+; CHECK-NEXT:    csel x0, xzr, x8, gt
+; CHECK-NEXT:    ret
+entry:
+  %cmp = icmp sgt i64 %a, %b
+  %. = select i1 %cmp, i64 0, i64 9223372036854775807
+  ret i64 %.
+}
+
 define i64 @foo19(i64 %a, i64 %b, i64 %c) {
 ; CHECK-LABEL: foo19:
 ; CHECK:       // %bb.0: // %entry
 ; CHECK-NEXT:    cmp x0, x1
 ; CHECK-NEXT:    cinc x0, x2, lo
 ; CHECK-NEXT:    ret
 entry:
   %cmp = icmp ult i64 %a, %b