[ARM][ParallelDSP] Fix self reference bug

[samparker]

Summary

Ensure we don't generate a smald intrinsic that takes itself as an argument.

github issue: https://github.com/llvm/llvm-project/issues/55899

[SjoerdMeijer]

LGTM

llvm/test/CodeGen/ARM/ParallelDSP/self-ref-bug.ll

3

Nit: do we need to run dce?

[fhahn]

LGTM, thanks!

llvm/lib/Target/ARM/ARMParallelDSP.cpp

case Instruction::Add: {
     Value *LHS = I->getOperand(0);
     Value *RHS = I->getOperand(1);
     bool ValidLHS = Search(LHS, BB, R);
     bool ValidRHS = Search(RHS, BB, R);
 
     if (ValidLHS && ValidRHS)
       return true;
 
+    // Ensure we don't add the root as the incoming accumulator.
+    if (R.getRoot() == I)
+      return false;
+
     return R.InsertAcc(I);
   }
   case Instruction::Mul: {
     Value *MulOp0 = I->getOperand(0);
     Value *MulOp1 = I->getOperand(1);
     return IsNarrowSequence<16>(MulOp0) && IsNarrowSequence<16>(MulOp1);
   }
   case Instruction::SExt:
for (Instruction &I : reverse(BB)) {
       LLVM_DEBUG(dbgs() << "After search, Reduction:\n"; R.dump());
 
       if (!CreateParallelPairs(R))
         continue;
 
       InsertParallelMACs(R);
       Changed = true;
       AllAdds.insert(R.getAdds().begin(), R.getAdds().end());
+      LLVM_DEBUG(dbgs() << "BB after inserting parallel MACs:\n" << BB);
     }
   }
 
   return Changed;
 }
 
 bool ARMParallelDSP::CreateParallelPairs(Reduction &R) {
 

llvm/test/CodeGen/ARM/ParallelDSP/self-ref-bug.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -mtriple=thumbv7-unknown-linux-gnueabihf < %s -arm-parallel-dsp -verify -S | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+
+define i32 @test(ptr %b) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = load i16, ptr [[B:%.*]], align 2
+; CHECK-NEXT:    [[TMP1:%.*]] = load i32, ptr [[B]], align 2
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i32 [[TMP1]] to i16
+; CHECK-NEXT:    [[TMP3:%.*]] = sext i16 [[TMP2]] to i32
+; CHECK-NEXT:    [[TMP4:%.*]] = lshr i32 [[TMP1]], 16
+; CHECK-NEXT:    [[TMP5:%.*]] = trunc i32 [[TMP4]] to i16
+; CHECK-NEXT:    [[TMP6:%.*]] = sext i16 [[TMP5]] to i32
+; CHECK-NEXT:    [[CONV:%.*]] = sext i16 [[TMP0]] to i32
+; CHECK-NEXT:    [[ARRAYIDX1:%.*]] = getelementptr inbounds i16, ptr [[B]], i32 3
+; CHECK-NEXT:    [[TMP7:%.*]] = load i16, ptr [[ARRAYIDX1]], align 2
+; CHECK-NEXT:    [[TMP8:%.*]] = load i32, ptr [[ARRAYIDX1]], align 2
+; CHECK-NEXT:    [[TMP9:%.*]] = trunc i32 [[TMP8]] to i16
+; CHECK-NEXT:    [[TMP10:%.*]] = call i32 @llvm.arm.smlad(i32 [[TMP8]], i32 [[TMP1]], i32 0)
+; CHECK-NEXT:    [[TMP11:%.*]] = sext i16 [[TMP9]] to i32
+; CHECK-NEXT:    [[TMP12:%.*]] = lshr i32 [[TMP8]], 16
+; CHECK-NEXT:    [[TMP13:%.*]] = trunc i32 [[TMP12]] to i16
+; CHECK-NEXT:    [[TMP14:%.*]] = sext i16 [[TMP13]] to i32
+; CHECK-NEXT:    [[CONV2:%.*]] = sext i16 [[TMP7]] to i32
+; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i32 [[TMP11]], [[TMP3]]
+; CHECK-NEXT:    [[INCDEC_PTR:%.*]] = getelementptr inbounds i16, ptr [[B]], i32 1
+; CHECK-NEXT:    [[TMP15:%.*]] = load i16, ptr [[INCDEC_PTR]], align 2
+; CHECK-NEXT:    [[CONV4:%.*]] = sext i16 [[TMP15]] to i32
+; CHECK-NEXT:    [[ARRAYIDX5:%.*]] = getelementptr inbounds i16, ptr [[B]], i32 4
+; CHECK-NEXT:    [[TMP16:%.*]] = load i16, ptr [[ARRAYIDX5]], align 2
+; CHECK-NEXT:    [[CONV6:%.*]] = sext i16 [[TMP16]] to i32
+; CHECK-NEXT:    [[MUL7:%.*]] = mul nsw i32 [[TMP14]], [[TMP6]]
+; CHECK-NEXT:    [[ADD9:%.*]] = add nsw i32 [[MUL7]], [[MUL]]
+; CHECK-NEXT:    [[MUL13:%.*]] = mul nsw i32 0, 0
+; CHECK-NEXT:    [[ADD15:%.*]] = add nsw i32 [[MUL13]], [[TMP10]]
+; CHECK-NEXT:    ret i32 [[ADD15]]
+;
+entry:
+  %0 = load i16, ptr %b, align 2
+  %conv = sext i16 %0 to i32
+  %arrayidx1 = getelementptr inbounds i16, ptr %b, i32 3
+  %1 = load i16, ptr %arrayidx1, align 2
+  %conv2 = sext i16 %1 to i32
+  %mul = mul nsw i32 %conv2, %conv
+  %incdec.ptr = getelementptr inbounds i16, ptr %b, i32 1
+  %2 = load i16, ptr %incdec.ptr, align 2
+  %conv4 = sext i16 %2 to i32
+  %arrayidx5 = getelementptr inbounds i16, ptr %b, i32 4
+  %3 = load i16, ptr %arrayidx5, align 2
+  %conv6 = sext i16 %3 to i32
+  %mul7 = mul nsw i32 %conv6, %conv4
+  %add9 = add nsw i32 %mul7, %mul
+  %mul13 = mul nsw i32 0, 0
+  %add15 = add nsw i32 %mul13, %add9
+  ret i32 %add15
+}