[llvm] [InstCombine] Increase recursion limit to 3 in `simplifyNonNullOperand` (PR #128695)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/128695

Address review comment https://github.com/llvm/llvm-project/pull/128466#discussion_r1967228790



>From 72781f58efddecee19feb07fec4e6104ef4c4812 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 25 Feb 2025 18:44:46 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.

---
 llvm/test/Transforms/InstCombine/load.ll | 32 ++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/load.ll b/llvm/test/Transforms/InstCombine/load.ll
index a5ad1e0c21526..ce6f64d658fe9 100644
--- a/llvm/test/Transforms/InstCombine/load.ll
+++ b/llvm/test/Transforms/InstCombine/load.ll
@@ -451,3 +451,35 @@ define i32 @load_select_with_null_gep(i1 %cond, ptr %p, i64 %off) {
   %res = load i32, ptr %gep, align 4
   ret i32 %res
 }
+
+define i16 @load_select_with_null_gep2(i1 %cond, ptr %p, i64 %x) {
+; CHECK-LABEL: @load_select_with_null_gep2(
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], ptr [[P:%.*]], ptr null
+; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr i8, ptr [[SEL]], i64 -2
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i16, ptr [[INVARIANT_GEP]], i64 [[X:%.*]]
+; CHECK-NEXT:    [[RES:%.*]] = load i16, ptr [[GEP]], align 2
+; CHECK-NEXT:    ret i16 [[RES]]
+;
+  %sel = select i1 %cond, ptr %p, ptr null
+  %invariant.gep = getelementptr i8, ptr %sel, i64 -2
+  %gep = getelementptr i16, ptr %invariant.gep, i64 %x
+  %res = load i16, ptr %gep, align 2
+  ret i16 %res
+}
+
+define i16 @load_select_with_null_ge3(i1 %cond, ptr %p, i64 %x, i64 %y) {
+; CHECK-LABEL: @load_select_with_null_ge3(
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], ptr [[P:%.*]], ptr null
+; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr i8, ptr [[SEL]], i64 -2
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i16, ptr [[INVARIANT_GEP]], i64 [[X:%.*]]
+; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr i16, ptr [[GEP]], i64 [[Y:%.*]]
+; CHECK-NEXT:    [[RES:%.*]] = load i16, ptr [[GEP2]], align 2
+; CHECK-NEXT:    ret i16 [[RES]]
+;
+  %sel = select i1 %cond, ptr %p, ptr null
+  %invariant.gep = getelementptr i8, ptr %sel, i64 -2
+  %gep = getelementptr i16, ptr %invariant.gep, i64 %x
+  %gep2 = getelementptr i16, ptr %gep, i64 %y
+  %res = load i16, ptr %gep2, align 2
+  ret i16 %res
+}

>From 3853aee61626b0eda06671b4cbbc4cdd1344440c Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 25 Feb 2025 18:59:14 +0800
Subject: [PATCH 2/2] [InstCombine] Increase recursion limit to 3 in
 `simplifyNonNullOperand`

---
 .../Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp   | 3 ++-
 llvm/test/Transforms/InstCombine/load.ll                    | 6 ++----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 622884ea1eb46..221511e9aba0b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -996,7 +996,8 @@ Value *InstCombinerImpl::simplifyNonNullOperand(Value *V,
   if (!V->hasOneUse())
     return nullptr;
 
-  if (Depth == 1)
+  constexpr unsigned RecursionLimit = 3;
+  if (Depth == RecursionLimit)
     return nullptr;
 
   if (auto *GEP = dyn_cast<GetElementPtrInst>(V)) {
diff --git a/llvm/test/Transforms/InstCombine/load.ll b/llvm/test/Transforms/InstCombine/load.ll
index ce6f64d658fe9..99185a4e6f043 100644
--- a/llvm/test/Transforms/InstCombine/load.ll
+++ b/llvm/test/Transforms/InstCombine/load.ll
@@ -454,8 +454,7 @@ define i32 @load_select_with_null_gep(i1 %cond, ptr %p, i64 %off) {
 
 define i16 @load_select_with_null_gep2(i1 %cond, ptr %p, i64 %x) {
 ; CHECK-LABEL: @load_select_with_null_gep2(
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], ptr [[P:%.*]], ptr null
-; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr i8, ptr [[SEL]], i64 -2
+; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr i8, ptr [[SEL:%.*]], i64 -2
 ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i16, ptr [[INVARIANT_GEP]], i64 [[X:%.*]]
 ; CHECK-NEXT:    [[RES:%.*]] = load i16, ptr [[GEP]], align 2
 ; CHECK-NEXT:    ret i16 [[RES]]
@@ -469,8 +468,7 @@ define i16 @load_select_with_null_gep2(i1 %cond, ptr %p, i64 %x) {
 
 define i16 @load_select_with_null_ge3(i1 %cond, ptr %p, i64 %x, i64 %y) {
 ; CHECK-LABEL: @load_select_with_null_ge3(
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND:%.*]], ptr [[P:%.*]], ptr null
-; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr i8, ptr [[SEL]], i64 -2
+; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr i8, ptr [[SEL:%.*]], i64 -2
 ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i16, ptr [[INVARIANT_GEP]], i64 [[X:%.*]]
 ; CHECK-NEXT:    [[GEP2:%.*]] = getelementptr i16, ptr [[GEP]], i64 [[Y:%.*]]
 ; CHECK-NEXT:    [[RES:%.*]] = load i16, ptr [[GEP2]], align 2