[llvm-branch-commits] [llvm] release/20.x: [ValueTracking] Skip incoming values that are the same as the phi in `isGuaranteedNotToBeUndefOrPoison` (#130111) (PR #130474)

[via llvm-branch-commits]

https://github.com/llvmbot updated https://github.com/llvm/llvm-project/pull/130474

>From f62b50e0e8f170412c95d7c1263c46a400bbeba8 Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Fri, 7 Mar 2025 05:46:32 +0800
Subject: [PATCH] [ValueTracking] Skip incoming values that are the same as the
 phi in `isGuaranteedNotToBeUndefOrPoison` (#130111)

Fixes (keep it open) #130110.

If the incoming value is PHI itself, we can skip this. If we can
guarantee that the other incoming values are neither undef nor poison,
then we can also guarantee that the value isn't either. If we cannot
guarantee that, it makes no sense in calculating it.

(cherry picked from commit 462eb7e28ef4507b16a4b45efb356bc6a3523615)
---
 llvm/lib/Analysis/ValueTracking.cpp          |  2 +
 llvm/test/Analysis/ValueTracking/phi-self.ll | 89 ++++++++++++++++++++
 2 files changed, 91 insertions(+)
 create mode 100644 llvm/test/Analysis/ValueTracking/phi-self.ll

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 4e79f41df2eb9..02a48d35a74aa 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -7777,6 +7777,8 @@ static bool isGuaranteedNotToBeUndefOrPoison(
       unsigned Num = PN->getNumIncomingValues();
       bool IsWellDefined = true;
       for (unsigned i = 0; i < Num; ++i) {
+        if (PN == PN->getIncomingValue(i))
+          continue;
         auto *TI = PN->getIncomingBlock(i)->getTerminator();
         if (!isGuaranteedNotToBeUndefOrPoison(PN->getIncomingValue(i), AC, TI,
                                               DT, Depth + 1, Kind)) {
diff --git a/llvm/test/Analysis/ValueTracking/phi-self.ll b/llvm/test/Analysis/ValueTracking/phi-self.ll
new file mode 100644
index 0000000000000..17afd872cab03
--- /dev/null
+++ b/llvm/test/Analysis/ValueTracking/phi-self.ll
@@ -0,0 +1,89 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instsimplify < %s | FileCheck %s
+
+; Test `%r` can be replaced by `%nonpoison`.
+
+define i32 @other_noundef(i32 noundef %arg) {
+; CHECK-LABEL: define i32 @other_noundef(
+; CHECK-SAME: i32 noundef [[ARG:%.*]]) {
+; CHECK-NEXT:  [[START:.*]]:
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[NONPOISON:%.*]] = phi i32 [ 0, %[[START]] ], [ [[NONPOISON]], %[[BB0:.*]] ], [ [[ARG]], %[[BB1:.*]] ]
+; CHECK-NEXT:    [[I:%.*]] = call i32 @opaque()
+; CHECK-NEXT:    switch i32 [[I]], label %[[EXIT:.*]] [
+; CHECK-NEXT:      i32 0, label %[[BB0]]
+; CHECK-NEXT:      i32 1, label %[[BB1]]
+; CHECK-NEXT:    ]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    ret i32 [[NONPOISON]]
+; CHECK:       [[BB0]]:
+; CHECK-NEXT:    br label %[[LOOP]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    br label %[[LOOP]]
+;
+start:
+  br label %loop
+
+loop:
+  %nonpoison = phi i32 [ 0, %start ], [ %nonpoison, %bb0 ], [ %arg, %bb1 ]
+  %i = call i32 @opaque()
+  switch i32 %i, label %exit [
+  i32 0, label %bb0
+  i32 1, label %bb1
+  ]
+
+exit:
+  %r = freeze i32 %nonpoison
+  ret i32 %r
+
+bb0:
+  br label %loop
+
+bb1:
+  br label %loop
+}
+
+define i32 @other_poison(i32 %arg) {
+; CHECK-LABEL: define i32 @other_poison(
+; CHECK-SAME: i32 [[ARG:%.*]]) {
+; CHECK-NEXT:  [[START:.*]]:
+; CHECK-NEXT:    br label %[[LOOP:.*]]
+; CHECK:       [[LOOP]]:
+; CHECK-NEXT:    [[MAYPOISON:%.*]] = phi i32 [ 0, %[[START]] ], [ [[MAYPOISON]], %[[BB0:.*]] ], [ [[ARG]], %[[BB1:.*]] ]
+; CHECK-NEXT:    [[I:%.*]] = call i32 @opaque()
+; CHECK-NEXT:    switch i32 [[I]], label %[[EXIT:.*]] [
+; CHECK-NEXT:      i32 0, label %[[BB0]]
+; CHECK-NEXT:      i32 1, label %[[BB1]]
+; CHECK-NEXT:    ]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    [[R:%.*]] = freeze i32 [[MAYPOISON]]
+; CHECK-NEXT:    ret i32 [[R]]
+; CHECK:       [[BB0]]:
+; CHECK-NEXT:    br label %[[LOOP]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    br label %[[LOOP]]
+;
+start:
+  br label %loop
+
+loop:
+  %maypoison = phi i32 [ 0, %start ], [ %maypoison, %bb0 ], [ %arg, %bb1 ]
+  %i = call i32 @opaque()
+  switch i32 %i, label %exit [
+  i32 0, label %bb0
+  i32 1, label %bb1
+  ]
+
+exit:
+  %r = freeze i32 %maypoison
+  ret i32 %r
+
+bb0:
+  br label %loop
+
+bb1:
+  br label %loop
+}
+
+declare i32 @opaque()