[llvm] [ValueTracking] Skip incoming values that are the same as the phi in `isGuaranteedNotToBeUndefOrPoison` (PR #130111)
via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 6 06:25:54 PST 2025
https://github.com/DianQK created https://github.com/llvm/llvm-project/pull/130111
Fixes #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.
>From e10b2baed2baad5d77473234d7d158f204ca2132 Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Thu, 6 Mar 2025 21:44:20 +0800
Subject: [PATCH 1/2] Add test cases
---
llvm/test/Analysis/ValueTracking/phi-self.ll | 146 +++++++++++++++++++
1 file changed, 146 insertions(+)
create mode 100644 llvm/test/Analysis/ValueTracking/phi-self.ll
diff --git a/llvm/test/Analysis/ValueTracking/phi-self.ll b/llvm/test/Analysis/ValueTracking/phi-self.ll
new file mode 100644
index 0000000000000..e9e61c27827f8
--- /dev/null
+++ b/llvm/test/Analysis/ValueTracking/phi-self.ll
@@ -0,0 +1,146 @@
+; 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 i64 @other_noundef() {
+; CHECK-LABEL: define i64 @other_noundef() {
+; CHECK-NEXT: [[START:.*]]:
+; CHECK-NEXT: br label %[[LOOP:.*]]
+; CHECK: [[LOOP]]:
+; CHECK-NEXT: [[NONPOISON:%.*]] = phi i64 [ [[NONPOISON]], %[[BB0:.*]] ], [ [[NONPOISON]], %[[BB1:.*]] ], [ [[NONPOISON]], %[[BB2:.*]] ], [ [[NONPOISON]], %[[BB:.*]] ], [ [[I:%.*]], %[[BACK_TO_LOOP:.*]] ], [ 0, %[[START]] ]
+; CHECK-NEXT: [[I]] = call i64 @opaque()
+; CHECK-NEXT: switch i64 [[I]], label %[[EXIT0:.*]] [
+; CHECK-NEXT: i64 -1, label %[[EXIT1:.*]]
+; CHECK-NEXT: i64 2, label %[[BACK_TO_LOOP]]
+; CHECK-NEXT: i64 0, label %[[BB]]
+; CHECK-NEXT: ]
+; CHECK: [[EXIT0]]:
+; CHECK-NEXT: br label %[[EXIT1]]
+; CHECK: [[EXIT1]]:
+; CHECK-NEXT: [[R:%.*]] = phi i64 [ [[NONPOISON]], %[[LOOP]] ], [ undef, %[[EXIT0]] ]
+; CHECK-NEXT: ret i64 [[R]]
+; CHECK: [[BACK_TO_LOOP]]:
+; CHECK-NEXT: br label %[[LOOP]]
+; CHECK: [[BB]]:
+; CHECK-NEXT: switch i64 [[NONPOISON]], label %[[LOOP]] [
+; CHECK-NEXT: i64 0, label %[[BB0]]
+; CHECK-NEXT: i64 1, label %[[BB1]]
+; CHECK-NEXT: i64 2, label %[[BB2]]
+; CHECK-NEXT: ]
+; CHECK: [[BB0]]:
+; CHECK-NEXT: br label %[[LOOP]]
+; CHECK: [[BB1]]:
+; CHECK-NEXT: br label %[[LOOP]]
+; CHECK: [[BB2]]:
+; CHECK-NEXT: br label %[[LOOP]]
+;
+start:
+ br label %loop
+
+loop: ; preds = %bb2, %bb1, %bb0, %bb, %back_to_loop, %start
+ %nonpoison = phi i64 [ %nonpoison, %bb0 ], [ %nonpoison, %bb1 ], [ %nonpoison, %bb2 ], [ %nonpoison, %bb ], [ %i, %back_to_loop ], [ 0, %start ]
+ %i = call i64 @opaque()
+ switch i64 %i, label %exit0 [
+ i64 -1, label %exit1
+ i64 2, label %back_to_loop
+ i64 0, label %bb
+ ]
+
+exit0: ; preds = %loop
+ br label %exit1
+
+exit1: ; preds = %exit0, %loop
+ %r = phi i64 [ %nonpoison, %loop ], [ undef, %exit0 ]
+ ret i64 %r
+
+back_to_loop: ; preds = %loop
+ br label %loop
+
+bb: ; preds = %loop
+ switch i64 %nonpoison, label %loop [
+ i64 0, label %bb0
+ i64 1, label %bb1
+ i64 2, label %bb2
+ ]
+
+bb0: ; preds = %bb
+ br label %loop
+
+bb1: ; preds = %bb
+ br label %loop
+
+bb2: ; preds = %bb
+ br label %loop
+}
+
+define i64 @other_poison() {
+; CHECK-LABEL: define i64 @other_poison() {
+; CHECK-NEXT: [[START:.*:]]
+; CHECK-NEXT: br label %[[LOOP:.*]]
+; CHECK: [[LOOP]]:
+; CHECK-NEXT: [[I:%.*]] = call i64 @opaque()
+; CHECK-NEXT: switch i64 [[I]], label %[[EXIT0:.*]] [
+; CHECK-NEXT: i64 -1, label %[[EXIT1:.*]]
+; CHECK-NEXT: i64 2, label %[[BACK_TO_LOOP:.*]]
+; CHECK-NEXT: i64 0, label %[[BB:.*]]
+; CHECK-NEXT: ]
+; CHECK: [[EXIT0]]:
+; CHECK-NEXT: br label %[[EXIT1]]
+; CHECK: [[EXIT1]]:
+; CHECK-NEXT: ret i64 0
+; CHECK: [[BACK_TO_LOOP]]:
+; CHECK-NEXT: br label %[[LOOP]]
+; CHECK: [[BB]]:
+; CHECK-NEXT: switch i64 0, label %[[LOOP]] [
+; CHECK-NEXT: i64 0, label %[[BB0:.*]]
+; CHECK-NEXT: i64 1, label %[[BB1:.*]]
+; CHECK-NEXT: i64 2, label %[[BB2:.*]]
+; CHECK-NEXT: ]
+; CHECK: [[BB0]]:
+; CHECK-NEXT: br label %[[LOOP]]
+; CHECK: [[BB1]]:
+; CHECK-NEXT: br label %[[LOOP]]
+; CHECK: [[BB2]]:
+; CHECK-NEXT: br label %[[LOOP]]
+;
+start:
+ br label %loop
+
+loop: ; preds = %bb2, %bb1, %bb0, %bb, %back_to_loop, %start
+ %maypoison = phi i64 [ %maypoison, %bb0 ], [ %maypoison, %bb1 ], [ %maypoison, %bb2 ], [ %maypoison, %bb ], [ poison, %back_to_loop ], [ 0, %start ]
+ %i = call i64 @opaque()
+ switch i64 %i, label %exit0 [
+ i64 -1, label %exit1
+ i64 2, label %back_to_loop
+ i64 0, label %bb
+ ]
+
+exit0: ; preds = %loop
+ br label %exit1
+
+exit1: ; preds = %exit0, %loop
+ %r = phi i64 [ %maypoison, %loop ], [ undef, %exit0 ]
+ ret i64 %r
+
+back_to_loop: ; preds = %loop
+ br label %loop
+
+bb: ; preds = %loop
+ switch i64 %maypoison, label %loop [
+ i64 0, label %bb0
+ i64 1, label %bb1
+ i64 2, label %bb2
+ ]
+
+bb0: ; preds = %bb
+ br label %loop
+
+bb1: ; preds = %bb
+ br label %loop
+
+bb2: ; preds = %bb
+ br label %loop
+}
+
+declare i64 @opaque()
>From d998eed8aae7cd8d5d28266c9c21f903a100e532 Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Tue, 4 Mar 2025 22:43:34 +0800
Subject: [PATCH 2/2] [ValueTracking] Skip incoming values that are the same as
the phi
---
llvm/lib/Analysis/ValueTracking.cpp | 2 ++
llvm/test/Analysis/ValueTracking/phi-self.ll | 5 ++---
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index e3e026f7979da..9b098bcb28bcc 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -7824,6 +7824,8 @@ 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
index e9e61c27827f8..095a16983ce21 100644
--- a/llvm/test/Analysis/ValueTracking/phi-self.ll
+++ b/llvm/test/Analysis/ValueTracking/phi-self.ll
@@ -8,7 +8,7 @@ define i64 @other_noundef() {
; CHECK-NEXT: [[START:.*]]:
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
-; CHECK-NEXT: [[NONPOISON:%.*]] = phi i64 [ [[NONPOISON]], %[[BB0:.*]] ], [ [[NONPOISON]], %[[BB1:.*]] ], [ [[NONPOISON]], %[[BB2:.*]] ], [ [[NONPOISON]], %[[BB:.*]] ], [ [[I:%.*]], %[[BACK_TO_LOOP:.*]] ], [ 0, %[[START]] ]
+; CHECK-NEXT: [[R:%.*]] = phi i64 [ [[R]], %[[BB0:.*]] ], [ [[R]], %[[BB1:.*]] ], [ [[R]], %[[BB2:.*]] ], [ [[R]], %[[BB:.*]] ], [ [[I:%.*]], %[[BACK_TO_LOOP:.*]] ], [ 0, %[[START]] ]
; CHECK-NEXT: [[I]] = call i64 @opaque()
; CHECK-NEXT: switch i64 [[I]], label %[[EXIT0:.*]] [
; CHECK-NEXT: i64 -1, label %[[EXIT1:.*]]
@@ -18,12 +18,11 @@ define i64 @other_noundef() {
; CHECK: [[EXIT0]]:
; CHECK-NEXT: br label %[[EXIT1]]
; CHECK: [[EXIT1]]:
-; CHECK-NEXT: [[R:%.*]] = phi i64 [ [[NONPOISON]], %[[LOOP]] ], [ undef, %[[EXIT0]] ]
; CHECK-NEXT: ret i64 [[R]]
; CHECK: [[BACK_TO_LOOP]]:
; CHECK-NEXT: br label %[[LOOP]]
; CHECK: [[BB]]:
-; CHECK-NEXT: switch i64 [[NONPOISON]], label %[[LOOP]] [
+; CHECK-NEXT: switch i64 [[R]], label %[[LOOP]] [
; CHECK-NEXT: i64 0, label %[[BB0]]
; CHECK-NEXT: i64 1, label %[[BB1]]
; CHECK-NEXT: i64 2, label %[[BB2]]
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