[llvm] [SLP][REVEC] Ignore UserTreeIndex if it is empty. (PR #131993)

[Han-Kuan Chen via llvm-commits]

https://github.com/HanKuanChen created https://github.com/llvm/llvm-project/pull/131993

Previously, the all_of check did not consider the case where the
TreeEntry is empty (i.e., when it is the first entry).

>From e92f2eee49ad3992aef3bbd0168add57830efffe Mon Sep 17 00:00:00 2001
From: Han-Kuan Chen <hankuan.chen at sifive.com>
Date: Wed, 19 Mar 2025 02:51:32 -0700
Subject: [PATCH 1/2] [SLP][REVEC] Pre-commit test.

---
 ...ec-reduced-value-replace-extractelement.ll | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)
 create mode 100644 llvm/test/Transforms/SLPVectorizer/X86/revec-reduced-value-replace-extractelement.ll

diff --git a/llvm/test/Transforms/SLPVectorizer/X86/revec-reduced-value-replace-extractelement.ll b/llvm/test/Transforms/SLPVectorizer/X86/revec-reduced-value-replace-extractelement.ll
new file mode 100644
index 0000000000000..2297eae416732
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/X86/revec-reduced-value-replace-extractelement.ll
@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S --passes=slp-vectorizer -slp-threshold=-99999 < %s -mtriple=x86_64-unknown-linux-gnu -slp-revec | FileCheck %s
+
+define void @test() {
+bb:
+  br label %bb1
+
+bb1:
+  %phi = phi i32 [ 0, %bb ], [ %mul9, %bb1 ]
+  %phi2 = phi i32 [ 0, %bb ], [ 0, %bb1 ]
+  %trunc = trunc i64 0 to i32
+  %mul = mul i32 0, %trunc
+  %mul3 = mul i32 %trunc, %phi
+  %mul4 = mul i32 %mul3, %mul
+  %mul5 = mul i32 %mul4, %mul
+  %trunc6 = trunc i64 0 to i32
+  %mul7 = mul i32 0, %trunc6
+  %mul8 = mul i32 %mul5, %mul7
+  %mul9 = mul i32 %mul8, %mul7
+  br label %bb1
+}

>From 23ad5592b4a54fff95a936b3e986bd06dcf2ee06 Mon Sep 17 00:00:00 2001
From: Han-Kuan Chen <hankuan.chen at sifive.com>
Date: Wed, 19 Mar 2025 02:49:49 -0700
Subject: [PATCH 2/2] [SLP][REVEC] Ignore UserTreeIndex if it is empty.

Previously, the all_of check did not consider the case where the
TreeEntry is empty (i.e., when it is the first entry).
---
 llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp    |  7 ++++---
 .../revec-reduced-value-replace-extractelement.ll  | 14 ++++++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index a2200f283168d..084da5607e400 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -6449,9 +6449,10 @@ void BoUpSLP::reorderTopToBottom() {
             assert(SLPReVec && "Only supported by REVEC.");
             // ShuffleVectorInst does not do reorderOperands (and it should not
             // because ShuffleVectorInst supports only a limited set of
-            // patterns). Only do reorderNodeWithReuses if all of the users are
-            // not ShuffleVectorInst.
-            if (isa<ShuffleVectorInst>(TE->UserTreeIndex.UserTE->getMainOp()))
+            // patterns). Only do reorderNodeWithReuses if the user is not
+            // ShuffleVectorInst.
+            if (TE->UserTreeIndex &&
+                isa<ShuffleVectorInst>(TE->UserTreeIndex.UserTE->getMainOp()))
               continue;
             assert((!TE->UserTreeIndex ||
                     !isa<ShuffleVectorInst>(
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/revec-reduced-value-replace-extractelement.ll b/llvm/test/Transforms/SLPVectorizer/X86/revec-reduced-value-replace-extractelement.ll
index 2297eae416732..bdd5971c0c91a 100644
--- a/llvm/test/Transforms/SLPVectorizer/X86/revec-reduced-value-replace-extractelement.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/revec-reduced-value-replace-extractelement.ll
@@ -2,6 +2,20 @@
 ; RUN: opt -S --passes=slp-vectorizer -slp-threshold=-99999 < %s -mtriple=x86_64-unknown-linux-gnu -slp-revec | FileCheck %s
 
 define void @test() {
+; CHECK-LABEL: define void @test() {
+; CHECK-NEXT:  [[BB:.*]]:
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i64 0 to i32
+; CHECK-NEXT:    br label %[[BB1:.*]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = phi <2 x i32> [ zeroinitializer, %[[BB]] ], [ [[TMP4:%.*]], %[[BB1]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = extractelement <2 x i32> [[TMP0]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = call i8 @llvm.vector.reduce.mul.v4i8(<4 x i8> zeroinitializer)
+; CHECK-NEXT:    [[TMP3:%.*]] = zext i8 [[TMP2]] to i32
+; CHECK-NEXT:    [[OP_RDX:%.*]] = mul i32 [[TMP3]], [[TMP1]]
+; CHECK-NEXT:    [[OP_RDX1:%.*]] = mul i32 [[OP_RDX]], [[TRUNC]]
+; CHECK-NEXT:    [[TMP4]] = insertelement <2 x i32> <i32 0, i32 poison>, i32 [[OP_RDX1]], i32 1
+; CHECK-NEXT:    br label %[[BB1]]
+;
 bb:
   br label %bb1