[AMDGPU] Handle CreateBinOp not returning BinaryOperator

AMDGPUCodeGenPrepareImpl::visitBinaryOperator() calls Builder.CreateBinOp()
and casts the resulting Value as a BinaryOperator without checking, leading
to an assert failure in a case found by fuzzing. In this case, the operands
are constant and CreateBinOp does constant folding so returns a Constant
instead of a BinaryOperator.

Author: anjenner

llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp

@@ -1685,7 +1685,10 @@ bool AMDGPUCodeGenPrepareImpl::visitBinaryOperator(BinaryOperator &I) {
             // return the new value. Just insert a scalar copy and defer
             // expanding it.
             NewElt = Builder.CreateBinOp(Opc, NumEltN, DenEltN);
-            Div64ToExpand.push_back(cast<BinaryOperator>(NewElt));
+            // CreateBinOp does constant folding. If the operands are constant,
+            // it will return a Constant instead of a BinaryOperator.
+            if (auto *NewEltBO = dyn_cast<BinaryOperator>(NewElt))
+              Div64ToExpand.push_back(NewEltBO);
           }
         }
 

llvm/test/CodeGen/AMDGPU/print-pipeline-passes.AFLCustomIRMutator.ll

@@ -0,0 +1,11 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx90a -O1 < %s | FileCheck -check-prefix=GCN %s
+
+define amdgpu_kernel void @kernel() {
+; GCN-LABEL: kernel:
+; GCN:       ; %bb.0: ; %entry
+; GCN-NEXT:    s_endpgm
+entry:
+  %B = srem <32 x i64> zeroinitializer, zeroinitializer
+  ret void
+}