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

[Yingwei Zheng via llvm-commits]

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

>From cd2d4fc4360b028587117fd4f91b8627976e960c 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 1/3] [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 d10aabff6709a..c6e28653e7fab 100644
--- a/llvm/test/Transforms/InstCombine/load.ll
+++ b/llvm/test/Transforms/InstCombine/load.ll
@@ -481,3 +481,32 @@ define i16 @load_select_with_null_gep3(i1 %cond, ptr %p, i64 %x, i64 %y) {
   %res = load i16, ptr %gep2, align 2
   ret i16 %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 3b13bda80ca0ad349105c59ed6087201b4c76899 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 2/3] [InstCombine] Simplify nonnull phi nodes

---
 .../InstCombine/InstCombineLoadStoreAlloca.cpp     | 14 ++++++++++++++
 llvm/test/Transforms/InstCombine/load.ll           |  4 +---
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 221511e9aba0b..52245a80cd4ef 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1011,6 +1011,20 @@ 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 c6e28653e7fab..736a31fc6ae0a 100644
--- a/llvm/test/Transforms/InstCombine/load.ll
+++ b/llvm/test/Transforms/InstCombine/load.ll
@@ -487,10 +487,8 @@ 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:

>From 3a27268e264826ef9cf493f645507e490f05e7f3 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 25 Feb 2025 23:44:36 +0800
Subject: [PATCH 3/3] [InstCombine] Address review comments.

---
 .../Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp    | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 52245a80cd4ef..c1f5e286ab3ed 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1014,8 +1014,9 @@ 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)) {
+      // We set Depth to RecursionLimit to avoid expensive recursion.
+      if (auto *Res = simplifyNonNullOperand(U.get(), HasDereferenceable,
+                                             RecursionLimit)) {
         replaceUse(U, Res);
         Changed = true;
       }