Fixed assertion in SROA if block has ho successors

[rampitec]

Summary

BasicBlock::isLegalToHoistInto() asserts if block does not
have successors. The case is degenarate but assertion still
needs to be avoided.

https://bugs.llvm.org/show_bug.cgi?id=46280

[arsenm]

llvm/lib/Transforms/Scalar/SROA.cpp

3484

succ_empty?

llvm/lib/Transforms/Scalar/SROA.cpp

bool foldGEPPhi(GetElementPtrInst &GEPI) {
     if (!GEPI.hasAllConstantIndices())
       return false;
 
     PHINode *PHI = cast<PHINode>(GEPI.getPointerOperand());
     if (GEPI.getParent() != PHI->getParent() ||
         llvm::any_of(PHI->incoming_values(), [](Value *In)
           { Instruction *I = dyn_cast<Instruction>(In);
             return !I || isa<GetElementPtrInst>(I) || isa<PHINode>(I) ||
+                   succ_begin(I->getParent()) == succ_end(I->getParent()) ||
                    !I->getParent()->isLegalToHoistInto();
           }))
       return false;
 
     LLVM_DEBUG(dbgs() << "  Rewriting gep(phi) -> phi(gep):"
                       << "\n    original: " << *PHI
                       << "\n              " << GEPI
                       << "\n          to: ");

llvm/test/Transforms/SROA/phi-gep.ll

 
 end:
   %phi_end = phi float* [ %gep_a_cast_to_float, %entry], [ %phi, %for ]
   %phi_end.1 = bitcast float* %phi_end to i32*
   %load = load i32, i32* %phi_end.1, align 4
   ret i32 %load
 }
 
+define void @unreachable_term() {
+; CHECK-LABEL: @unreachable_term(
+; CHECK-NEXT:    [[A_SROA_0:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    [[A_SROA_0_0_A_SROA_CAST1:%.*]] = bitcast i32* [[A_SROA_0]] to [3 x i32]*
+; CHECK-NEXT:    unreachable
+; CHECK:       bb1:
+; CHECK-NEXT:    br label [[BB1_I:%.*]]
+; CHECK:       bb1.i:
+; CHECK-NEXT:    [[PHI:%.*]] = phi [3 x i32]* [ [[A_SROA_0_0_A_SROA_CAST1]], [[BB1:%.*]] ], [ null, [[BB1_I]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr [3 x i32], [3 x i32]* [[PHI]], i64 0, i64 0
+; CHECK-NEXT:    store i32 0, i32* [[GEP]], align 1
+; CHECK-NEXT:    br i1 undef, label [[BB1_I]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    br label [[BB2:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    ret void
+;
+  %a = alloca [3 x i32], align 1
+  unreachable
+
+bb1:
+  br label %bb1.i
+
+bb1.i:
+  %phi = phi [3 x i32]* [ %a, %bb1 ], [ null, %bb1.i ]
+  %gep = getelementptr [3 x i32], [3 x i32]* %phi, i64 0, i64 0
+  store i32 0, i32* %gep, align 1
+  br i1 undef, label %bb1.i, label %exit
+
+exit:
+  br label %bb2
+
+bb2:
+  ret void
+}
+
 declare %pair* @foo()
 
 declare i32 @__gxx_personality_v0(...)