[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 created https://github.com/llvm/llvm-project/pull/130474

Backport 462eb7e28ef4507b16a4b45efb356bc6a3523615

Requested by: @nikic

>From 92c994999ad85f0d115d7abe30b1ab3f6d79552d 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 8a674914641a8..43013294e2b4c 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -7776,6 +7776,8 @@ 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()