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

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/98155

Fixes https://github.com/llvm/llvm-project/issues/98139.


>From 955e15ae7d7a32654eb2795208009e8240e5dc5f Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 9 Jul 2024 20:51:51 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests from PR98139. NFC.

---
 llvm/test/Transforms/InstCombine/pr98139.ll | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 llvm/test/Transforms/InstCombine/pr98139.ll

diff --git a/llvm/test/Transforms/InstCombine/pr98139.ll b/llvm/test/Transforms/InstCombine/pr98139.ll
new file mode 100644
index 0000000000000..563427df8c15c
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pr98139.ll
@@ -0,0 +1,20 @@
+; 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:    [[TMP1:%.*]] = trunc i16 [[A]] to i8
+; CHECK-NEXT:    [[TRUNC:%.*]] = xor i8 [[TMP1]], -1
+; 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
+}

>From d45001a9d1efe5a1cfe2c1519b3a8c40b50a6a02 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 9 Jul 2024 21:15:18 +0800
Subject: [PATCH 2/2] [InstCombine] Fix typo in `adjustKnownBitsForSelectArm`

---
 .../InstCombine/InstCombineSimplifyDemanded.cpp        |  2 +-
 llvm/test/Transforms/InstCombine/pr98139.ll            | 10 ++++++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 98f085a2c756a..081e783c964fd 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/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;
diff --git a/llvm/test/Transforms/InstCombine/pr98139.ll b/llvm/test/Transforms/InstCombine/pr98139.ll
index 563427df8c15c..4c1d9d55562d4 100644
--- a/llvm/test/Transforms/InstCombine/pr98139.ll
+++ b/llvm/test/Transforms/InstCombine/pr98139.ll
@@ -4,8 +4,14 @@
 define i8 @pr98139(i16 %a, i16 %b, i1 %cond) {
 ; CHECK-LABEL: define i8 @pr98139(
 ; CHECK-SAME: i16 [[A:%.*]], i16 [[B:%.*]], i1 [[COND:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i16 [[A]] to i8
-; CHECK-NEXT:    [[TRUNC:%.*]] = xor i8 [[TMP1]], -1
+; 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