[AArch64][SelectionDAG] Mask for SUBS with multiple users cannot be e…

…lided (#90911)

In DAGCombiner, the `performCONDCombine` function attempts to remove AND
instructions in front of SUBS (cmp) instructions for which the AND is
transparent. The rules for that are correct, but it fails to take into
account the case where the SUBS instruction has multiple users with
different condition codes for comparison and simply removes the AND for
all of them. This causes a miscompilation in the attached test case.

(cherry picked from commit 72eaa0e)

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -22122,7 +22122,8 @@ SDValue performCONDCombine(SDNode *N,
   SDNode *SubsNode = N->getOperand(CmpIndex).getNode();
   unsigned CondOpcode = SubsNode->getOpcode();
 
-  if (CondOpcode != AArch64ISD::SUBS || SubsNode->hasAnyUseOfValue(0))
+  if (CondOpcode != AArch64ISD::SUBS || SubsNode->hasAnyUseOfValue(0) ||
+      !SubsNode->hasOneUse())
     return SDValue();
 
   // There is a SUBS feeding this condition. Is it fed by a mask we can

llvm/test/CodeGen/AArch64/and-mask-removal.ll

@@ -526,4 +526,26 @@ define i64 @pr58109b(i8 signext %0, i64 %a, i64 %b) {
   ret i64 %4
 }
 
+define i64 @test_2_selects(i8 zeroext %a) {
+; CHECK-LABEL: test_2_selects:
+; CHECK:       ; %bb.0:
+; CHECK-NEXT:    add w9, w0, #24
+; CHECK-NEXT:    mov w8, #131
+; CHECK-NEXT:    and w9, w9, #0xff
+; CHECK-NEXT:    cmp w9, #81
+; CHECK-NEXT:    mov w9, #57
+; CHECK-NEXT:    csel x8, x8, xzr, lo
+; CHECK-NEXT:    csel x9, xzr, x9, eq
+; CHECK-NEXT:    add x0, x8, x9
+; CHECK-NEXT:    ret
+  %1 = add i8 %a, 24
+  %2 = zext i8 %1 to i64
+  %3 = icmp ult i8 %1, 81
+  %4 = select i1 %3, i64 131, i64 0
+  %5 = icmp eq i8 %1, 81
+  %6 = select i1 %5, i64 0, i64 57
+  %7 = add i64 %4, %6
+  ret i64 %7
+}
+
 declare i8 @llvm.usub.sat.i8(i8, i8) #0