[llvm] [InstCombine] Simplify nonnull phi nodes (PR #128466)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/128466

Fix some regressions caused by https://github.com/llvm/llvm-project/pull/128111.


>From 353cb5334842a6969f9958f1548110a33c143de8 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 24 Feb 2025 13:35:19 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.

---
 llvm/test/Transforms/InstCombine/load.ll | 29 ++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/load.ll b/llvm/test/Transforms/InstCombine/load.ll
index a5ad1e0c21526..c356c6ce3948e 100644
--- a/llvm/test/Transforms/InstCombine/load.ll
+++ b/llvm/test/Transforms/InstCombine/load.ll
@@ -451,3 +451,32 @@ define i32 @load_select_with_null_gep(i1 %cond, ptr %p, i64 %off) {
   %res = load i32, ptr %gep, align 4
   ret i32 %res
 }
+
+define i32 @test_load_phi_with_select(ptr %p, i1 %cond1) {
+; CHECK-LABEL: @test_load_phi_with_select(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP_BODY:%.*]]
+; CHECK:       loop.body:
+; CHECK-NEXT:    [[BASE:%.*]] = phi ptr [ [[P1:%.*]], [[ENTRY:%.*]] ], [ [[P:%.*]], [[LOOP_BODY]] ]
+; CHECK-NEXT:    [[TARGET:%.*]] = getelementptr inbounds nuw i8, ptr [[BASE]], i64 24
+; CHECK-NEXT:    [[LOAD:%.*]] = load i32, ptr [[TARGET]], align 4
+; CHECK-NEXT:    [[P]] = select i1 [[COND1:%.*]], ptr null, ptr [[P1]]
+; CHECK-NEXT:    [[COND21:%.*]] = icmp eq i32 [[LOAD]], 0
+; CHECK-NEXT:    br i1 [[COND21]], label [[LOOP_BODY]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 [[LOAD]]
+;
+entry:
+  br label %loop.body
+
+loop.body:
+  %base = phi ptr [ %p, %entry ], [ %sel, %loop.body ]
+  %target = getelementptr inbounds i8, ptr %base, i64 24
+  %load = load i32, ptr %target, align 4
+  %sel = select i1 %cond1, ptr null, ptr %p
+  %cond2 = icmp eq i32 %load, 0
+  br i1 %cond2, label %loop.body, label %exit
+
+exit:
+  ret i32 %load
+}

>From c213cfd89a4a4ead8516351e136a4c572fd4de28 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 24 Feb 2025 13:55:53 +0800
Subject: [PATCH 2/2] [InstCombine] Simplify nonnull phi nodes

---
 .../InstCombine/InstCombineLoadStoreAlloca.cpp   | 16 +++++++++++++++-
 llvm/test/Transforms/InstCombine/load.ll         |  4 +---
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 622884ea1eb46..e7dd0858ac687 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -996,7 +996,7 @@ Value *InstCombinerImpl::simplifyNonNullOperand(Value *V,
   if (!V->hasOneUse())
     return nullptr;
 
-  if (Depth == 1)
+  if (Depth == 2)
     return nullptr;
 
   if (auto *GEP = dyn_cast<GetElementPtrInst>(V)) {
@@ -1010,6 +1010,20 @@ Value *InstCombinerImpl::simplifyNonNullOperand(Value *V,
     }
   }
 
+  if (auto *PHI = dyn_cast<PHINode>(V)) {
+    bool Changed = false;
+    for (Use &U : PHI->incoming_values()) {
+      if (auto *Res =
+              simplifyNonNullOperand(U.get(), HasDereferenceable, Depth + 1)) {
+        replaceUse(U, Res);
+        Changed = true;
+      }
+    }
+    if (Changed)
+      addToWorklist(PHI);
+    return nullptr;
+  }
+
   return nullptr;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/load.ll b/llvm/test/Transforms/InstCombine/load.ll
index c356c6ce3948e..891e3a031b711 100644
--- a/llvm/test/Transforms/InstCombine/load.ll
+++ b/llvm/test/Transforms/InstCombine/load.ll
@@ -457,10 +457,8 @@ define i32 @test_load_phi_with_select(ptr %p, i1 %cond1) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP_BODY:%.*]]
 ; CHECK:       loop.body:
-; CHECK-NEXT:    [[BASE:%.*]] = phi ptr [ [[P1:%.*]], [[ENTRY:%.*]] ], [ [[P:%.*]], [[LOOP_BODY]] ]
-; CHECK-NEXT:    [[TARGET:%.*]] = getelementptr inbounds nuw i8, ptr [[BASE]], i64 24
+; CHECK-NEXT:    [[TARGET:%.*]] = getelementptr inbounds nuw i8, ptr [[BASE:%.*]], i64 24
 ; CHECK-NEXT:    [[LOAD:%.*]] = load i32, ptr [[TARGET]], align 4
-; CHECK-NEXT:    [[P]] = select i1 [[COND1:%.*]], ptr null, ptr [[P1]]
 ; CHECK-NEXT:    [[COND21:%.*]] = icmp eq i32 [[LOAD]], 0
 ; CHECK-NEXT:    br i1 [[COND21]], label [[LOOP_BODY]], label [[EXIT:%.*]]
 ; CHECK:       exit: