[llvm] Fix crash caused by reprocessing complex reductions (#122077)

If a complex pattern had the shape of both a complex->complex reduction
and a complex->single reduction, the matching would recognise both and
deem the graph a valid transformation. Preventing this reprocessing
results in only one of these matching, meaning that in the case of an
invalid graph, we don't try to transform it anyway.

Author: NickGuy-Arm

llvm/lib/CodeGen/ComplexDeinterleavingPass.cpp

@@ -1730,7 +1730,7 @@ void ComplexDeinterleavingGraph::identifyReductionNodes() {
     auto *Real = OperationInstruction[i];
     // We want to check that we have 2 operands, but the function attributes
     // being counted as operands bloats this value.
-    if (Real->getNumOperands() < 2)
+    if (Processed[i] || Real->getNumOperands() < 2)
       continue;
 
     RealPHI = ReductionInfo[Real].first;

llvm/test/CodeGen/AArch64/complex-deinterleaving-opt-crash.ll

@@ -0,0 +1,35 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S --passes=complex-deinterleaving %s --mattr=+sve2 | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-ni:1-p2:32:8:8:32-ni:2"
+target triple = "aarch64-arm-none-linux"
+
+; Ensure that a second reduction-like pattern doesn't override the first
+; We don't care what this IR produces, just that it produces something and doesn't cause a crash
+define void @reprocessing_crash() #0 {
+; CHECK-LABEL: define void @reprocessing_crash
+;
+entry:
+  br label %vector.body
+
+vector.body:                                      ; preds = %vector.body, %entry
+  %vec.phi18 = phi <vscale x 2 x double> [ zeroinitializer, %entry ], [ %2, %vector.body ]
+  %vec.phi20 = phi <vscale x 2 x double> [ zeroinitializer, %entry ], [ %3, %vector.body ]
+  %strided.vec22 = tail call { <vscale x 2 x double>, <vscale x 2 x double> } @llvm.vector.deinterleave2.nxv4f64(<vscale x 4 x double> zeroinitializer)
+  %0 = extractvalue { <vscale x 2 x double>, <vscale x 2 x double> } %strided.vec22, 0
+  %1 = extractvalue { <vscale x 2 x double>, <vscale x 2 x double> } %strided.vec22, 1
+  %2 = fsub <vscale x 2 x double> %vec.phi18, %0
+  %3 = fsub <vscale x 2 x double> %vec.phi20, %1
+  br i1 false, label %middle.block, label %vector.body
+
+middle.block:                                     ; preds = %vector.body
+  %bin.rdx = fadd <vscale x 2 x double> %2, zeroinitializer
+  %bin.rdx23 = fadd <vscale x 2 x double> %3, zeroinitializer
+  ret void
+}
+
+; Function Attrs: nocallback nofree nosync nounwind willreturn memory(none)
+declare { <vscale x 2 x double>, <vscale x 2 x double> } @llvm.vector.deinterleave2.nxv4f64(<vscale x 4 x double>) #1
+
+attributes #0 = { "target-cpu"="neoverse-v1" }
+attributes #1 = { nocallback nofree nosync nounwind willreturn memory(none) }