[llvm] [InstCombine] Drop noundef attributes in `foldCttzCtlz` (PR #116718)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/116718

Closes https://github.com/llvm/llvm-project/issues/112068.

>From 2ac20c7523093b1b91d4216ee0c630b7c3e22bd8 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 19 Nov 2024 08:40:01 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.

---
 .../Transforms/InstCombine/shift-cttz-ctlz.ll    | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll b/llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll
index 1c381d08390715..dd614595c42f73 100644
--- a/llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll
+++ b/llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll
@@ -15,6 +15,22 @@ entry:
   ret i32 %res
 }
 
+; Make sure that noundef is dropped.
+
+define i32 @shl_cttz_false_noundef(i32 %x, i32 %y) {
+; CHECK-LABEL: define i32 @shl_cttz_false_noundef(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CTTZ:%.*]] = call noundef range(i32 0, 33) i32 @llvm.cttz.i32(i32 [[Y]], i1 true)
+; CHECK-NEXT:    [[RES:%.*]] = shl i32 [[X]], [[CTTZ]]
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+entry:
+  %cttz = call noundef i32 @llvm.cttz.i32(i32 %y, i1 false)
+  %res = shl i32 %x, %cttz
+  ret i32 %res
+}
+
 define i32 @shl_ctlz_false(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i32 @shl_ctlz_false(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {

>From eb7feac6683c15de1d193e59fb4b694340fc83de Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 19 Nov 2024 08:59:13 +0800
Subject: [PATCH 2/2] [InstCombine] Drop noundef attributes in `foldCttzCtlz`

---
 llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp | 4 +++-
 llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll  | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 6cff3c7af91e32..42c0acd1e45ec1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -505,8 +505,10 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombinerImpl &IC) {
 
   // If ctlz/cttz is only used as a shift amount, set is_zero_poison to true.
   if (II.hasOneUse() && match(Op1, m_Zero()) &&
-      match(II.user_back(), m_Shift(m_Value(), m_Specific(&II))))
+      match(II.user_back(), m_Shift(m_Value(), m_Specific(&II)))) {
+    II.dropUBImplyingAttrsAndMetadata();
     return IC.replaceOperand(II, 1, IC.Builder.getTrue());
+  }
 
   Constant *C;
 
diff --git a/llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll b/llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll
index dd614595c42f73..63caec95013254 100644
--- a/llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll
+++ b/llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll
@@ -21,7 +21,7 @@ define i32 @shl_cttz_false_noundef(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i32 @shl_cttz_false_noundef(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[CTTZ:%.*]] = call noundef range(i32 0, 33) i32 @llvm.cttz.i32(i32 [[Y]], i1 true)
+; CHECK-NEXT:    [[CTTZ:%.*]] = call range(i32 0, 33) i32 @llvm.cttz.i32(i32 [[Y]], i1 true)
 ; CHECK-NEXT:    [[RES:%.*]] = shl i32 [[X]], [[CTTZ]]
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;