[InstCombine] Fix typo in adjustKnownBitsForSelectArm (llvm#98155)

Fixes llvm#98139.

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

@@ -411,7 +411,7 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Instruction *I,
     // Only known if known in both the LHS and RHS.
     adjustKnownBitsForSelectArm(LHSKnown, I->getOperand(0), I->getOperand(1),
                                 /*Invert=*/false, Depth, Q);
-    adjustKnownBitsForSelectArm(LHSKnown, I->getOperand(0), I->getOperand(2),
+    adjustKnownBitsForSelectArm(RHSKnown, I->getOperand(0), I->getOperand(2),
                                 /*Invert=*/true, Depth, Q);
     Known = LHSKnown.intersectWith(RHSKnown);
     break;

llvm/test/Transforms/InstCombine/pr98139.ll

@@ -0,0 +1,26 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+define i8 @pr98139(i16 %a, i16 %b, i1 %cond) {
+; CHECK-LABEL: define i8 @pr98139(
+; CHECK-SAME: i16 [[A:%.*]], i16 [[B:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND]], i16 1, i16 254
+; CHECK-NEXT:    [[COND1:%.*]] = icmp ne i16 [[B]], 0
+; CHECK-NEXT:    [[MASK:%.*]] = and i16 [[A]], 255
+; CHECK-NEXT:    [[COND2:%.*]] = icmp ne i16 [[MASK]], 255
+; CHECK-NEXT:    [[COND3:%.*]] = or i1 [[COND1]], [[COND2]]
+; CHECK-NEXT:    [[SEL2:%.*]] = select i1 [[COND3]], i16 [[SEL]], i16 255
+; CHECK-NEXT:    [[SUB:%.*]] = sub i16 [[SEL2]], [[A]]
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i16 [[SUB]] to i8
+; CHECK-NEXT:    ret i8 [[TRUNC]]
+;
+  %sel = select i1 %cond, i16 1, i16 254
+  %cond1 = icmp ne i16 %b, 0
+  %mask = and i16 %a, 255
+  %cond2 = icmp ne i16 %mask, 255
+  %cond3 = or i1 %cond1, %cond2
+  %sel2 = select i1 %cond3, i16 %sel, i16 255
+  %sub = sub i16 %sel2, %a
+  %trunc = trunc i16 %sub to i8
+  ret i8 %trunc
+}